Lexical Definition

‎εὔκαιρος‎ eúkairos (yoo'-kahee-ros) opportune G:A
from ‎εὖ‎ and ‎καιρός‎

convenient, in time of need.

Usage: 3 forms in 3 verses
Form Translated As     In Verse(s)
εὔκαιρον in time of need Heb.4.16
εὐκαίρου opportune Mark.6.21
εύκαιρον an opportune time LXX.Ps.104.27

Abbott-Smith

εὔ-καιρος, -ον [in LXX: Ps 103 (104):27* (עֵת), II Mac 14:29 15:20, 21, III Mac 4:11 5:44 * ;]
timely, seasonable, suitable (Cremer, 740): ἡμέρα, Mk 6:21 (or empty, as in Byz. and MGr.; v. MM, Exp., xiv); βοήθεια, He 4:16.†

Abbott-Smith References

Book Refs
Psalms 104:27*
Mark 6:21
Hebrews 4:16

Liddell-Scott-Jones

εὔκαιρος-ος, ον,

well-timed, seasonable, λόγος [Refs 4th c.BC+]; ὕδατα (rainfall) [Refs 4th c.BC+]; nihil -ότερον epistula tua, [Refs 1st c.BC+]: with infinitive, χὥ τι σοι λέγειν εὔκαιροςόν ἐστι [Refs 5th c.BC+]; τὸ εὔκαιροςον, ={εὐκαιρία}, [Refs 1st c.BC+]; εὔκαιροςον ἀείσας in season, [Refs 5th c.BC+]

__II of places, convenient, well situated, τόποι [Refs 3rd c.BC+]
__III rich, wealthy, uncertain reading in St. Byzantine see at {Χαττηνία}.
__IV adverb -ρως seasonably, opportunely, [Refs 5th c.BC+]; εὐ. χρῆσθαί τινι [Refs 5th c.BC+]; favourably, propitiously, [Refs 3rd c.BC+]: comparative -ότερον [Refs 5th c.BC+]: superlative -ότατα [Refs 2nd c.BC+]
__IV.2 οὐκ-ρως ἔχειν to have no leisure, [Refs]