an established custom: an accepted, repeated way of doing things that a group takes for granted
TranslatabilityDirectCertaintySettled
At its simplest this word names an established way of doing things, a practice a group has settled into and takes for granted. In John's account of Jesus' trial it is the standing arrangement by which the governor releases a prisoner at Passover, an accepted usage rather than a written law. In Paul's closing word on worship it is the settled practice of the churches, the shared habit of how God's people do things together.
The word is built from a root meaning "together" or "with," and that gives it its particular flavor: a custom is something done in company and repeated over time, so its authority comes from long, shared use rather than from any formal decree. Two neighboring words sharpen the picture. ἔθος is a custom that can carry legal or religious weight, and παράδοσις is a tradition deliberately handed down; this word, by contrast, leans on the quiet force of what a community has simply grown used to.
Nuances
1aa public or civic custom: an accepted, unofficial usage rather than a written law
Jhn 18:39*
Jhn 18:39
Whether the Passover custom of releasing a prisoner, which this verse attributes to the crowd ("you have a custom"), reflects a real practice in Roman Judea, and if so whose custom it originally was.
majorityA genuine, if informal, release practice lies behind the scene; some argue it began as a Jewish custom that the Romans continued, which would make John's "your custom" historically apt. Brown grants a historical kernel while doubting any formal Roman legal instrument.; Charles B. Chavel, "The Releasing of a Prisoner on the Eve of Passover in Ancient Jerusalem," JBL 60 (1941): 273-78; Craig S. Keener, The Gospel of John: A Commentary (Hendrickson, 2003), 2.1113-17; D. A. Carson, The Gospel According to John, PNTC (Eerdmans, 1991), 594-95
minorityNo such established custom existed; the notice is legendary or dramatized, with at most a single Barabbas incident behind it.; Paul Winter, On the Trial of Jesus, 2nd ed. (de Gruyter, 1974), 94
1ba shared practice of a community, here the settled practice of the churches
1Co 11:16*
1Co 11:16
What the phrase "such custom" (τοιαύτην συνήθειαν) refers to in Paul's closing line about head coverings.
majority"Such custom" is the practice Paul has been arguing against (praying or prophesying with the head uncovered); he ends by appealing to the universal practice of the churches.; Gordon D. Fee, The First Epistle to the Corinthians, rev. ed., NICNT (Eerdmans, 2014), ad loc.; Anthony C. Thiselton, The First Epistle to the Corinthians, NIGTC (Eerdmans, 2000), ad loc.; David E. Garland, 1 Corinthians, BECNT (Baker, 2003), ad loc.
minority"Such custom" is the enforced head-covering rule itself, which Paul is relativizing rather than endorsing.; Alan Padgett, "Paul on Women in the Church: The Contradictions of Coiffure in 1 Corinthians 11.2-16," JSNT 20 (1984): 69-86; Cynthia Long Westfall, Paul and Gender (Baker, 2016), on 1 Cor 11:2-16
minority"Such custom" means being contentious; Paul says neither he nor the churches have a practice of quarreling.; John Chrysostom, Homilies on 1 Corinthians (noted in Robertson and Plummer, ICC, ad loc.)
2
being accustomed to something: the ingrained habit of a former way of life that still shapes a person
TranslatabilityPartialCertaintyStrong
Here the same word turns inward. It no longer describes an outward practice but a person's ingrained habit, the residual pull of a former way of life that still shapes how someone feels and reacts. Paul uses it for converts out of idol worship whose lifelong immersion in that world has left a mark their new faith has not yet erased. When they eat food that had been offered to an idol, an old reflex makes them feel it is still sacred, and their conscience is wounded.
Paul's point is subtle: the problem is not what these believers know but what they are used to. They understand that an idol is nothing, yet the habit of the heart lags behind the conviction of the head. (Some later manuscripts, followed by the King James Version, read "conscience" here instead of this word; the earliest and best manuscripts have this word, and modern scholarship treats that as the original reading.)
the same word can turn inward to name a person's ingrained habit, not only an outward group practice1Co 8:7
Both
both name an established, repeated way of doing things that a group takes for grantedJhn 18:391Co 11:16
Only custom
in English "custom" can suggest a formal institution or an official tradition, heavier and more fixed than the informal, lived practice the Greek names
“practice”
Comparison data is not available for this English gloss yet.
“accustomed”
Comparison data is not available for this English gloss yet.
How sunētheia differs from similar Greek words
ἔθοςa custom that can carry legal or religious force, such as the customs of Moses; this word is lived, ingrained practice with no such official weight.
Points to habit built up by repeated exposure, an inner accustoming rather than a rule laid down: those long used to idols still feel the food is really offered to one.1Co 8:7
Both
Both name a settled group practice, the accepted way a people or the churches do (or refuse to do) a thing.Jhn 19:401Co 11:16
Both can attach to a festival, naming the customary practice observed around it.Luk 2:42Jhn 18:39
Carries legal and civic force: the fixed practices that Roman law recognizes and that govern how officials must act.Act 16:21Act 25:16
Names sacred ordinances handed down as binding, above all the customs Moses delivered and the practices of the ancestors.Act 6:14Act 28:17
Reaches down to fixed liturgical routine and even a single person's regular practice, such as the priestly duty assigned by lot.Luk 1:9Luk 22:39
παράδοσιςa tradition deliberately handed down from one generation or teacher to the next; this word is a habit built up quietly by repeated use rather than consciously passed on.
It is a settled way of doing things that has grown up through repeated use rather than being formally passed on: the governor's standing habit of releasing a prisoner at the feast (John 18:39).Jhn 18:39
It can describe a personal habituation, a long familiarity that shapes how someone thinks and reacts: those who, through their earlier habit around idols, still eat with the idol on their mind (1 Corinthians 8:7).1Co 8:7
Both
Both name an accepted, group-level practice that carries weight and can be cited to settle how people ought to behave: the elders' handed-down tradition governs how hands are washed (Mark 7:5), and the churches' custom is invoked to end an argument over practice (1 Corinthians 11:16).Mrk 7:51Co 11:16
It names teaching or practice that is consciously handed down from one party to another, so the act of delivering and receiving is built into the word itself: what the elders passed to the next generation (Mark 7:5), what Paul says he delivered and told the church to hold onto (1 Corinthians 11:2).Mrk 7:51Co 11:2
It is tied to identifiable transmitters and often stands as a body of authoritative content weighed against Scripture: the tradition of the elders (Mark 7:3), the traditions of the fathers (Galatians 1:14), the tradition of men set against God's command (Colossians 2:8).Mrk 7:3Gal 1:14Col 2:8
What scholars say about sunētheia
συνήθεια is formed from σύν ("with, together") plus a noun related to ἔθος/ἦθος ("custom, character"), and the prefix gives it the sense of shared or sustained habituation. The standard lexicons agree on a twofold analysis for the New Testament. BDAG assigns John 18:39 and 1 Cor 11:16 to sense 1 ("custom, habit, usage") and 1 Cor 8:7 to sense 2 ("being accustomed to something," taking a genitive of the thing one is used to); Louw and Nida make the same split across domains 41.25 and 27.54, and LSJ files 1 Cor 8:7 under "habit" with the gloss "by being used to it." The pattern of συνήθεια plus an objective genitive ("habituation to X") is well attested in Xenophon, Demosthenes, and Aeschines. TDNT has no independent article (Preisker treats the word under ἔθος) and stresses that, unlike ἔθος, συνήθεια carries no sacral force in the New Testament: it is descriptive and, at 1 Cor 8:7, psychological. Spicq argues that the unifying thread is the σύν-, the shared or cumulative weight of habit, whether within a community (1 Cor 11:16) or within a single person (1 Cor 8:7). At 1 Cor 8:7 the reading συνηθείᾳ is preferred over the Byzantine συνειδήσει ("conscience") by Metzger and by every major modern commentator, who explain the variant as a scribal harmonization to the συνείδησις later in the same verse. The word does not occur in the Old Greek of the Hebrew Bible; its four occurrences in 4 Maccabees lean toward "companionship, familiarity" rather than "custom."
In-depth research
This is a research paper, so it may be hard to read without scholarly background. It is useful if you want to dig even deeper into this word.
LSJ (Liddell-Scott-Jones, 9th ed. with revised Supplement), s.v. συνήθειαlexicon
Louw and Nida, Greek-English Lexicon of the New Testament Based on Semantic Domains (UBS, 1988), sections 27.54 and 41.25lexicon
Ceslas Spicq, Theological Lexicon of the New Testament (Hendrickson, 1994), vol. 3, s.v. συνήθειαtheological dictionary
Heinrich Preisker, "ἔθος, ἦθος, συνήθεια," in TDNT 2 (Eerdmans, 1964), 372-75theological dictionary
Horst Balz and Gerhard Schneider, eds., Exegetical Dictionary of the New Testament (Eerdmans, 1990-93), vol. 3, p. 302, s.v. συνήθειαtheological dictionary
Bruce M. Metzger, A Textual Commentary on the Greek New Testament, 2nd ed. (1994), on 1 Cor 8:7reference
Gordon D. Fee, The First Epistle to the Corinthians, rev. ed., NICNT (Eerdmans, 2014)commentary
Anthony C. Thiselton, The First Epistle to the Corinthians, NIGTC (Eerdmans, 2000), 640-46commentary
Craig S. Keener, The Gospel of John: A Commentary (Hendrickson, 2003), 2.1113-17commentary
Raymond E. Brown, The Death of the Messiah (Doubleday, 1994), 1.793-820monograph
Alan Padgett, "Paul on Women in the Church," JSNT 20 (1984): 69-86journal article