Abbott-Smith Manual Greek Lexicon
ὄρθρος (G3722)
3 ὄρθρος , -ου, ὁ , [in LXX for שַׁחַר , בֹּקֶר , etc.;] daybreak , dawn : ὄρθρου βαθέως (M, Pr. , 73), at early dawn , Lk 24:1 ; ὄρθρου , Jo 8:[2] ; ὑπὸ τὸν ὄ. , Ac 5:21 (cf. MM, xviii).†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain