Abbott-Smith Manual Greek Lexicon
εὔ-καιρος (G2121)
2 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 .†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain