Quick Definition
ἀληθεύω v. I say, speak truth, I do truth
Strong's Definition
from 227; to be true (in doctrine and profession)
KJV Usage: speak (tell) the truth
UBS Dictionary of the Greek New Testament
verb | ἀ- + λήθω
33.251 · Communication · Speak Truth, Speak Falsehood
to speak the truth, to tell the truth to communicate what is true In a number of languages it may be difficult to employ a highly abstract term such as ‘truth.’ Accordingly, one may find it necessary to relate ‘truth’ in GAL 4:16 to the immediate context, for example, ‘... by telling you what they really want to do’ or ‘... what all this really means.’
UBS Dictionary of the Greek New Testament © United Bible Societies, licensed CC BY-SA 4.0.
Thayer's Greek Lexicon
ἀληθεύω ; in prof. writ. ([Aeschyl.], Xen., Plat., Aristot., al.) fo speak the truth; a. to teach the truth: τινί Gal. iv. 16. b. to profess the truth (true doctrine) : Eph. iv. 15. [R. V. mrg. in both pass. to deal truly.]
Mounce Concise Greek Dictionary
ἀληθεύω alētheuō 2x
to speak or maintain the truth; to act truly or sincerely, Gal. 4:16; Eph. 4:15*
Abbott-Smith Greek Lexicon
ἀληθεύω
(< ἀληθής), [in LXX: Ge 20:16 (יָכַח) Ge 42:16 (אֶמֶת), Pr 21:3 (מִשְׁפָּט), Is 44:26 (שָׁלַם), Si 34:4*;]
to speak the truth (R, mg., deal truly; Field, Notes, 192): Ga 4:16, Eph 4:15.†
Moulton & Milligan — Vocabulary of the Greek NT
ἀληθεύω. We have noticed no early occurrence, but cf. P. Amh II. 142! (iv/A.D.) a]AnBevovt . . ., before a gap.
Liddell-Scott-Jones — Greek-English Lexicon
ἀληθεύω (alētheuō) — be truthful. ἀληθ-εύω, future -εύσω[Refs 5th c.BC+]:—speak truth, [Refs 5th c.BC+]adjective, ἀ. πάντα speak truth in all things, [Refs 5th c.BC+]; τὰς δέκα ἡμέρας ἠλήθευσε he rightly foretold.. , [Refs]; ἀ. τοὺς ἐπαίνους prove their praises true, [Refs 2nd c.AD+]; τοὔνομα `make good', [Refs 4th c.AD+]
2. of things, to be, prove true, σημεῖα[Refs 5th c.BC+]:—passive, to be fulfilled, of conditions, ἐπὶ τούτοις -ομένοις[Refs 5th c.BC+]:—active of reasoners, arrive at truth, [Refs]:—passive, ὁ λόγος -εύεται is in accordance with truth, Top. [Refs]; ἀληθεύεσθαι κατά τινος to be truly predicated of.., [Refs]future middle in same sense, [Refs]