Quick Definition
I say, speak truth, I do truth
Strong's Definition
to be true (in doctrine and profession)
Derivation: from G227 (ἀληθής);
KJV Usage: speak (tell) the truth
Thayer's Greek Lexicon
ἀληθεύω; in secular writings ((Aeschylus), Xenophon, Plato, Aristotle, others) to speak the truth;
a. to teach the truth: τίνι Gal_4:16.
b. to profess the truth (true doctrine): Eph_4:15. (R. V. marginal reading in both passages, 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 : Gen_20:16 ( H3198 ) Gen_42:16 ( H571 ), Pro_21:3 ( H4941 ), Isa_44:26 ( H7999 ), Sir_34:4 * ;]
to speak the truth ( R , mg ., deal truly; Field, Notes , 192): Gal_4:16 , Eph_4:15 .†
Moulton & Milligan — Vocabulary of the Greek NT
ἀληθεύω [page 21]
We have noticed no early occurrence, but cf. P. Amh II. 142 .1 (iv/A.D.) ἀ ]ληθευοντ . . ., before a gap.
Liddell-Scott — Intermediate Greek Lexicon
ἀληθεύω [Etym: ἀληθής] "to speak truth", Aesch. , etc.; τὰς δέκα ἡμέρας ἠλήθευσε "he was right about" the 10 days, Xen. ; ἀλ. τοὺς ἐπαίνους "to prove" their praises true, Luc. Pass. "to come true", of predictions, Xen.
STEPBible — Tyndale Abridged Greek Lexicon
ἀληθεύω
(ἀληθής), [in LXX: Gen.20:16 (יָכַח) Gen.42:16 (אֶמֶת), Pro.21:3 (מִשְׁפָּט), Isa.44:26 (שָׁלַם), Sir.34:4 * ;]
to speak the truth (R, mg., deal truly; Field, Notes, 192): Gal.4:16, Eph.4:15.†
(AS)