At its heart this verb means to speak what a person knows is false. The New Testament uses it in two closely related ways: for lying in general, and for lying to someone in particular, where the falsehood is aimed at deceiving a specific person.
The most pointed case of the second is the account of Ananias, who is charged with having lied not merely to people but "to the Holy Spirit" and "to God." The verb is the same ordinary word for lying; what makes the moment weighty is the one being lied to.
The word also carries a positive force when it is negated. "I am not lying" becomes a way of swearing that what follows is true, and the claim that God "cannot lie" rests on this same verb: to say that God never speaks falsehood is to ground the trustworthiness of his promises. It stands at the center of a small family of falsehood words, alongside the noun for a lie itself (ψεῦδος) and the word for a liar (ψεύστης).
Names the act of lying, and usually names the one being lied to as well: Ananias lied to the Holy Spirit and so to God rather than to people, and believers are told to stop lying to each other.Act 5:3Act 5:4Col 3:9
It is the word a writer uses to swear that his own account is honest, saying flatly "I am not lying" about something he has just claimed.Rom 9:12Co 11:31Gal 1:201Ti 2:7
It covers false speech aimed at a target: evil spoken against people because they follow Jesus, and a false claim to be something one is not.Mat 5:11Rev 3:9
Because it is an act, it can be ruled out of someone's character entirely: it is the one thing God is unable to do.Heb 6:18
Both
Both are measured against the truth and defined as its opposite: claiming to share God's life while walking in darkness makes the claim false and leaves the truth undone, and nothing false comes out of the truth at all.1Jn 1:61Jn 2:21
Both carry the same instruction to the church about honest speech, one telling believers to quit lying to one another as part of taking off the old way of life, the other telling them to put falsehood away and speak the truth with their neighbour.Col 3:9Eph 4:25
Both are used to show where a being finally stands, since God is incapable of it while the devil is its father and speaks it from his own nature.Heb 6:18Jhn 8:44
Both name a lie that is not merely private dishonesty but a boast or a claim set against the truth of the gospel, whether in someone bragging over a rivalry inside the church or in a false teaching that has nothing true in it.Jas 3:141Jn 2:27
Names the falsehood itself as a thing, so it can be traded for something else and then believed: people swapped the truth about God for it, and are handed over to trusting it.Rom 1:252Th 2:11
In its heaviest uses it is not just any falsehood but one great counterfeit with a source behind it: the devil speaks it out of what he is and fathers it, and it stamps the fake wonders of the coming lawless one.Jhn 8:442Th 2:9
Being a thing, it can be present or absent in a person, which makes it a test of who belongs: none was found in the mouths of the redeemed, while everyone who loves and practises it is left outside the city.Rev 14:5Rev 21:27Rev 22:15
It is treated as a whole category, the flat opposite of truth: nothing of it comes out of the truth, and a teaching that is true is described by saying it is not this.1Jn 2:211Jn 2:27
ψεύστηςthe person, a liar, one whose settled character is to speak falsehood, where this verb is the act.
Names the act of lying itself, something a person does on a particular occasion, so the text can say who was lied to.Act 5:3Act 5:4Col 3:9
Carries a solemn denial in which a writer swears before God that what he has just said is true, saying in effect "I am not lying".Rom 9:12Co 11:31Gal 1:201Ti 2:7
Because it names an action and not a character, it can state the one thing God is unable to do.Heb 6:18
Covers false speech aimed at damaging someone else, and a false claim people make about their own identity.Mat 5:11Rev 3:9
Both
Both name deliberate falsehood, speech the speaker knows is untrue, and both are set directly against the truth.Jas 3:14Jhn 8:44
Both turn up where a claim to know or love God is tested against how the person actually lives, and the claim is exposed as false.1Jn 1:61Jn 4:20
Both measure people against God's own truthfulness, which is the fixed point the falsehood is judged by.Heb 6:18Rom 3:4
Names the person rather than the act: a verdict on who someone is, not a report of what he did on one occasion.Jhn 8:551Jn 2:41Jn 2:221Jn 4:20
Labels a whole group or a class of people, whether a nation's reputation, a list of the kinds of people sound teaching stands against, or the human race set over against God.Rom 3:41Ti 1:10Tit 1:12
Used in the charge that refusing what God has said makes God himself out to be untruthful.1Jn 1:101Jn 5:10
πλανάωto lead astray or deceive, the broader act of causing someone to go wrong, of which lying is one method.
Names the ACT of speaking a falsehood: asserting to someone what the speaker knows is untrue.Act 5:3Act 5:4Col 3:9
Used for solemnly affirming that one is telling the truth, "I am not lying", a claim about the honesty of one's own speech that has no parallel in a word about wandering.Rom 9:1Gal 1:201Ti 2:7
Used of being lied about, when people say untrue things against someone. The falsehood is carried entirely by words.Mat 5:11Rev 3:9
Both
Both stand as the opposite of "the truth" and appear as warnings against falsehood taking hold in the believer: lying and being deceived are two ways of failing to walk in the truth.1Jn 1:61Jn 1:8
Names the RESULT of being led wrong: a person wanders off and ends up lost, whether or not any lie was told. The picture is a straying sheep, not a spoken falsehood.Mat 18:12Mat 18:131Pe 2:25
Describes false teachers, false prophets, and Satan actively pulling crowds off course, so that people follow the wrong way. The aim is to move someone, not merely to make a false statement.Mat 24:4Mat 24:11Mrk 13:5Rev 12:9
Used of simply being mistaken or in the wrong, with no lie involved at all: a person can be "deceived" by their own ignorance of Scripture.Mat 22:29Heb 5:2Jas 1:16
pseudomai in the other biblical languages
כָּזַבHebrew“to lie”the main Hebrew verb for lying, telling a deliberate falsehood, often used of false witnesses and of promises that prove empty.
carries the apostolic oath formula where a writer solemnly affirms his own truthfulness, swearing before God that he does not lieRom 9:12Co 11:31Gal 1:201Ti 2:7
names lying as a mark of the old self that believers are to strip off, and of those who falsely claim an identity they do not holdCol 3:91Jn 1:6Rev 3:9
Both
both anchor the great denial that God cannot lie, holding up his faithfulness against human unreliabilityNum 23:19Heb 6:18
both describe lying directed at God himself, flattering or deceiving him with the tongue rather than merely deceiving a neighborPsa 78:36Act 5:4
Centers on the spoken word itself, on something said that is not true. It covers speaking evil against someone falsely, claiming a false identity, and professing one thing while living another.Mat 5:11Rev 3:91Jn 1:6
Carries the solemn first-person denial "I lie not", where a speaker swears before God that his own words are true. The Hebrew word is never turned into this oath of truthful speech.Rom 9:12Co 11:31Gal 1:201Ti 2:7
Both
Both stand for falsehood toward one another, and English Bibles render each as "lie": the Hebrew forbids Israel to "lie one to another" in the law, just where the Greek tells the church "Lie not one to another".Lev 19:11Col 3:9
Both are used to insist that God himself is utterly true: the Hebrew says the Strength of Israel "will not lie", and the Greek says it is impossible for God to lie.1Sa 15:29Heb 6:18
Reaches past a false statement to breaking faith, to betraying a person or an oath one is bound to keep. Abimelech asks Abraham to swear he will not "deal falsely" with him, and the people plead that they have not "dealt falsely" in God's covenant.Gen 21:23Psa 44:17
Describes a whole people proving false to the One who trusted them, a betrayal of relationship rather than a single spoken lie: God looked for children who "would not deal falsely".Isa 63:8
Names purely the verbal act of asserting what is false, to tell a lie in wordsCol 3:91Jn 1:6Rev 3:9
Appears in solemn oath formulas where the speaker swears he is not lying, staking his own truthfulness before GodRom 9:1Gal 1:202Co 11:31
Both
Both name the plain offense of lying to another person, and the New Testament command not to lie to one another echoes the Old Testament law against itLev 19:11Col 3:9
Both extend to lying against or denying God himself, the gravest form of falsehoodPro 30:9Act 5:4
Reaches beyond speech to denying a fact or deed under pressure, refusing to admit what one has doneGen 18:15Lev 6:2
Carries the distinctive sense of feigning submission, where a beaten enemy cringes and pretends loyalty to a conqueror2Sa 22:45Psa 18:44Psa 66:3Psa 81:15
Extends to physical failing or proving false, as when a crop yields nothing or a place disowns a manHab 3:17Job 8:18
What scholars say about pseudomai
The lexica treat ψεύδομαι as a settled item meaning to speak falsehood, to lie, with a well-attested transitive use "lie to, impose upon" taking the person deceived as object (BDAG). LSJ documents the same range from classical Greek onward. In the New Testament the word clusters in oath-strengthening negations (Paul's "I am not lying," Rom 9:1;2 Cor 11:31;Gal 1:20;1 Tim 2:7) and in the theologically loaded charge of Acts 5:3-4, where Ananias is said to have lied to the Holy Spirit and to God. Conzelmann's TDNT article on the ψεῦδος word group sets the term within the biblical opposition between truth and the lie, and notes the affirmation of God's truthfulness in Heb 6:18. The sense is not contested; the interest lies in usage rather than definition.
Sources
BDAG (Bauer-Danker), s.v. ψεύδομαιlexicon
LSJ (Liddell-Scott-Jones), s.v. ψεύδωlexicon
Hans Conzelmann, "ψεῦδος, ψεύδομαι, κτλ.," in Theological Dictionary of the New Testament (TDNT), vol. 9dictionary
Horst Balz and Gerhard Schneider, eds., Exegetical Dictionary of the New Testament (EDNT), s.v. ψεύδομαιdictionary