to call upon: to address someone directly, above all to invoke God or the Lord by name in prayer and worship
TranslatabilityApproximateCertaintySettled
This is the word's most weighty use in the New Testament. To call upon the Lord is to turn to him out loud and by name, appealing to him for rescue, help, or acceptance. It is the language of prayer and worship, and it carries the whole weight of trust: the people of God are described simply as those who call on his name.
The same reaching-out can be aimed at God in a particular role. A believer calls on God as Father, or calls on him to serve as witness to the truth of what one says. In every case the action is a deliberate, spoken appeal directed at a person who can answer.
A closely related turn of phrase runs the other direction: a name is called upon a group of people, meaning they are marked as belonging to the one whose name it is. When Scripture says God's name is called over the nations, or that the honorable name was called over believers, it means they have become his own and bear his stamp.
Nuances
1ato call on the Lord by name: to invoke God for salvation and in worship
1bto call on God in a particular role: to address him as Father, or to summon him as witness
2Co 1:231Pe 1:17
1cto have a name called over you: to be marked out as belonging to the one whose name it is
Act 15:17Jas 2:7
2
to name or nickname: to give someone an added name, or (in the passive) to be known by that name
TranslatabilityApproximateCertaintySettled
Used of a person, the word attaches a second name to someone: a surname, a nickname, or the familiar name by which they were known. It usually appears in a form that describes the person on the receiving end, as in Simon who was called Peter, John who was also called Mark, or Joseph who was surnamed Barnabas.
The naming can be hostile as well as neutral. When opponents pinned the name Beelzebul on Jesus, they were labeling him with a slur. The same construction can even describe God: he is not ashamed to be called their God, that is, to let his name be attached to his people as their own.
Nuances
2ato give or bear an added name: a surname, nickname, or familiar name
Mat 10:3Act 1:23Act 4:36Act 10:5Act 10:18Act 10:32Act 11:13Act 12:12Act 12:25
2bto pin a name or label on someone, including as an insult
Mat 10:25
2cto be called (a title): to have a name or title attached to oneself
Heb 11:16
3
to appeal: to formally invoke the judgment of a higher authority, above all a Roman citizen's appeal to Caesar
TranslatabilityApproximateCertaintySettled
In a legal setting the word names a formal act: a person under trial invokes a higher court and asks to be judged there instead. In the New Testament this is always Paul's appeal to Caesar, the right of a Roman citizen to have his case moved to the emperor's tribunal. Once the appeal was lodged it could not be undone, which is why Festus tells Paul that since he has appealed to Caesar, to Caesar he will go.
This is the same basic idea as calling on someone, but turned into a technical legal move: instead of calling on God for help, the accused calls on the emperor for a verdict.
names the specific Roman legal right of a citizen to have his case moved to the emperor's courtAct 25:11Act 25:12
Both
both invoke a higher authority to take up one's caseAct 28:19
Only appeal
modern English "appeal" usually means asking a higher court to review a decision already made, whereas here it is the initial demand to be tried before Caesar at all
How epikaleō differs from similar Greek words
καλέωthe plain verb "to call" (to summon, to invite, or to name); the word here adds the sense of calling upon or onto someone, hence invoking or surnaming
At its core this word means to call on someone by name, above all to call on the name of the Lord in worship and appeal. It is a naming word: the speaker invokes a specific person.Act 2:21Rom 10:13Act 22:16
It carries an everyday, non-religious use that the other word never has: to give or bear a name, to be surnamed or nicknamed.Mat 10:3Act 1:23Act 4:36
It also serves as a formal legal term: to appeal to a higher authority, as Paul appeals to Caesar. This is calling upon a person for a verdict, not prayer.Act 25:11Act 25:12Act 28:19
Both
Both can name the church at prayer, addressing God together. In the same scene the believers are gathered praying while Peter is delivered, and calling on the Lord names the very worship they are engaged in.Act 12:12
This is the ordinary, broad word for praying itself, the whole activity of speaking to God rather than the act of naming him. It covers set times and sustained sessions of prayer.Mat 6:5Mrk 1:35Luk 6:12
It readily takes an object of who or what one prays for, including praying for other people and even for enemies, which the naming word does not do.Mat 5:44Luk 6:28
It describes the posture, place, and content of prayer, such as kneeling, withdrawing to pray, and how one should pray.Mat 26:39Luk 11:1Luk 18:1
It is the word for prayer that turns to God by name and asks him to save or to receive the one praying.Act 2:21Rom 10:13Act 7:59
It carries a formal legal sense: appealing past a lower court to the emperor for a verdict.Act 25:11Act 25:12Act 28:19
It can summon God himself as the witness who guarantees that what the speaker says is true.2Co 1:23
Both
Both report the name a person actually goes by, whether the second name a disciple is known by or the new name given to him.Act 1:23Luk 6:14
Both describe the name of the Lord being pronounced over people, whether by believers who belong to that name or by outsiders trying to wield it.Act 9:14Act 19:13
Both can pin a label onto someone, fixing what that person is called in the eyes of others.Mat 10:251Co 5:11
It is the act of conferring a title on people at the moment they are appointed, giving the group its official designation.Mrk 3:14Luk 6:13
It can mean simply mentioning something out loud, which is why a practice can be forbidden even to be spoken of among God's people.Eph 5:31Co 5:1
It describes whether a name is yet spoken and known in a place, marking territory where Christ has not been preached.Rom 15:20
It can trace where a name comes from, so that every family owes its identity to the one it is named after.Eph 3:15
epikaleō in the other biblical languages
קָרָאHebrew“to call: call to”the Hebrew verb behind the Old Testament phrase "to call on the name of the LORD," which this Greek word carries into the New Testament
Carries a courtroom sense the Hebrew word never has: to appeal a case to a higher authority. Paul uses it to demand that his trial go to Caesar.Act 25:11Act 25:21Act 28:19
Its most weighted use is invoking the Lord in worship: to call on the name of Jesus, or on God, for salvation. It becomes a near-technical marker for being a believer.Act 2:21Rom 10:131Co 1:2
Both
Both name the act of calling on the LORD in worship, invoking his name. The Old Testament pattern of calling on the name of the LORD is exactly what the New Testament word picks up.Gen 4:26Gen 12:8Act 2:21Rom 10:13
Both can attach a name to someone. The Hebrew word gives Isaac his name at birth, and the Greek word marks the extra name a person is known by, such as Simon who was surnamed Peter.Gen 21:3Act 1:23Act 10:5
Ranges far wider than the Greek word: it also means to summon a person, to proclaim aloud, and to read a text out. It is the everyday verb for any kind of calling.Gen 24:57Gen 24:58
Actively gives a name: God calls the light Day and the darkness Night, and Adam calls the animals. The Greek word only takes on a name passively, as a surname added to someone.Gen 1:5Gen 2:19Gen 2:20
What scholars say about epikaleō
The lexica treat ἐπικαλέω as a single verb whose sense is fixed by voice and context (BDAG, s.v.; LSJ, s.v.). In the active and passive it means to give or bear an added name (surname, nickname), the most frequent New Testament use, especially in Acts. In the middle it means to call upon, invoke: pre-eminently to call on the name of the Lord, a formula taken over from the Septuagint rendering of Hebrew qara' be-shem YHWH (Joel 3:5 LXX, cited at Acts 2:21 and Romans 10:13). The idiom "the name is called over/upon someone" (Acts 15:17;James 2:7) likewise reflects Septuagint usage denoting ownership or belonging. A specialized middle sense, to appeal (to a higher tribunal, here Caesar), is a technical term of Roman legal procedure and is confined in the New Testament to Paul's trial narrative (Acts 25 through 28). See further the discussions of καλέω and its compounds in TDNT and the entry in EDNT.
Sources
BDAG, s.v. ἐπικαλέωlexicon
LSJ, s.v. ἐπικαλέωlexicon
K. L. Schmidt, 'καλέω κτλ.', TDNT 3:496-536dictionary