to lie: to say what is untrue, or (of a thing) to prove false and let one down
TranslatabilityApproximateCertaintySettled
At its heart this verb means to be false. A person who lies says what does not match reality, but the Hebrew stretches the same idea to any thing that fails to deliver what was expected. A spring that dries up, a promise left unkept, a vision that never arrives: each of these can be said to "lie."
So the word runs along two tracks that share one root idea. Most often it describes a speaker who tells an untruth, whether an ordinary lie, a false witness in court, or a prophet inventing a message. But it also describes a thing that proves unreliable and lets down the one who counted on it.
Closely related verbs sharpen different angles of falsehood. שׁקר leans on breaking faith and betraying a trust, while כחשׁ leans on denying or covering up what is true. This word centers on the gap itself: the claim, or the thing, simply does not hold up.
Nuances
1ato tell a lie: to say what one knows is untrue, or to be exposed as a liar
Names a source, hope, or promise that proves false and fails to deliver what it seemed to offer, such as a spring that runs dry or a vision that could disappoint.Isa 58:11Hab 2:3Job 41:9
Covers the false oracle and the deceiving prophet, words announced as true that are not, along with the lying tongue.Ezk 13:19Mic 2:11Psa 78:36
Both
Both stand behind the assurance that God does not lie, so that what he promises he will not take back.Num 23:191Sa 15:29
Names breaking faith within a sworn bond, dealing treacherously with someone you are pledged to rather than merely misstating a fact.Gen 21:23Psa 44:17Isa 63:8
כחשׁto deceive by denying or covering up what is true, where this word stresses asserting what is untrue or failing to hold up
Names a spoken falsehood itself: to utter what is untrue, to be a liar. The focus is the statement, not its victim, so it covers the witness who testifies falsely and the tongue that lies.Pro 14:5Psa 78:36
Predicated of God and his word by denial, to insist on their reliability: God is not a man, that he should lie, and his promise or vision will not prove false.Num 23:19Psa 89:35Hab 2:3
Extends past speech to a thing that fails to deliver what it seemed to promise, as of a spring whose waters run dry.Isa 58:11
Both
Both are rendered "deceive" and can describe false words aimed at misleading someone: the people deceiving God with their mouths, and the serpent deceiving Eve.Psa 78:36Gen 3:13
Lulls a person into false confidence, always working on someone's trust: the serpent draws Eve in, and Assyria's spokesmen tell Judah not to let Hezekiah or their God lure them into false hope.Gen 3:132Ki 18:292Ki 19:10
Describes self-deception, when a person's own pride or sense of security misleads them into a confidence that will collapse.Oba 1:3Jer 49:16
Marks false prophets and counselors who mislead a whole people into expecting an outcome that will not come.Jer 29:8Jer 4:10
Falsehood as emptiness and worthlessness: a thing with no substance behind it, not only an untrue statement.Psa 60:11Psa 127:1
The fixed term for empty worship and worthless idols, the religion that has nothing real behind it.Isa 1:13Jon 2:8
Stands in legal language for a false oath or false witness: swearing or testifying to what is groundless.Exo 20:7Deu 5:20
kazav in the other biblical languages
ψεύδομαιGreek“to lie”the standard Greek verb for lying, close to this word but almost entirely about false speech, where the Hebrew also covers things that prove false
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
It reaches past speech to anything that fails to hold up. A stream "whose waters do not fail" is described with this word, so is a hope about the great sea creature that proves empty, and so is a promised vision that will not disappoint when its time comes. English "liar" cannot stretch that far.Isa 58:11Job 41:9Hab 2:3
It is the word for handing on a false message as though it came from God. Prophets are condemned for speaking falsely to the people, and a windbag who promises wine and strong drink is exactly the preacher such a people wants.Ezk 13:19Mic 2:11
It names something a person does to another person in the moment, so it can be begged off, repented of, or ruled out in advance. Elisha is asked not to raise a false hope, Israel is charged with flattering God with their tongues, and a trustworthy witness is defined as one who will not do it.2Ki 4:16Psa 78:36Pro 14:5
Both
Both carry the sweeping verdict that human beings as a whole cannot be trusted to speak truth. The psalm says in haste that everyone is false, and Paul takes up that very line in Greek with this word when he insists God be found true and everyone else a liar.Psa 116:11Rom 3:4
Both fix God as the one exception, and both make refusing his word an accusation against him. God is not a man that he should lie, and he swears he will not break faith with David; on the Greek side, claiming to be sinless or refusing his testimony about his Son is said to make God himself a liar.Num 23:19Psa 89:351Jn 1:101Jn 5:10
Both supply the charge that a person's stated claim does not match the truth about them. Job demands to know who can prove him false and asks his friends not to speak falsely to his face; John says the person who claims to know God but ignores his commands, or claims to love God while hating a brother, is a liar.Job 24:25Job 6:281Jn 2:41Jn 4:20
It is a name for a kind of person, a label for what someone is rather than a word for something someone did on one occasion. Jesus calls the devil "a liar and the father of lies", Paul quotes a saying that the people of Crete are "always liars", and "liars" stand as a class of people in a list of wrongdoers.Jhn 8:44Tit 1:121Ti 1:10
It settles who a person really is on the basis of one confession about Jesus. Whoever denies that Jesus is the Christ is named a liar, and Jesus says that if he denied knowing the Father he would be a liar like those arguing with him.1Jn 2:22Jhn 8:55
What scholars say about kazav
The lexicons treat כזב as a single root meaning "to lie, be a liar," with a well-attested extension to things that prove deceptive or fail (BDB; HALOT). The personal sense dominates: telling an untruth (Numbers 23:19), bearing false witness (Proverbs 14:5), and false prophecy (Ezekiel 13:19;Micah 2:11). The intensive and derived forms yield nuances such as being proved a liar (Proverbs 30:6,Job 24:25). The figurative extension to a water source that fails (Isaiah 58:11) and to an unfulfilled vision or hope (Habakkuk 2:3;Job 41:9) is widely recognized and underlies the derived adjective used of a deceptive brook (H0391). Klopfenstein's study in TDOT places the term within the broader vocabulary of deception, distinguishing it from שׁקר and כחשׁ.
Sources
HALOT, s.v. כזבlexicon
BDB, s.v. כזבlexicon
TWOT §970 (kāzab)lexicon
M. A. Klopfenstein, "כָּזַב kāzab," in TDOT, vol. 7reference