Lexical Definition

‎ὀρθρινός‎ orthrinós (or-thrin-os') dawn ^G:A
from ‎ὄρθρος‎

morning.

• relating to the dawn, i.e. matutinal (as an epithet of Venus, especially brilliant in the early day)

Abbott-Smith

† ὀρθρινός, -ή, -όν (< ὄρθρος), [in LXX: Ho 6: (4) 13:3 (שׁכם hi.), Hg 2:15 (14), Wi 11:22*;] late form of ὄρθριος (q.v.),
early: Lk 24:22.†

Abbott-Smith References

Liddell-Scott-Jones

ὀρθρινός-ινός, ή, όν,

(ὄρθρος) later form [LXX+5th c.BC+]; ὀρθρινόςινὸς οἴχεσθαι [Refs 1st c.BC+] adverb, ὀρθρινόςινὰ παίζειν[Refs 4th c.BC+], etc. make ι long, probably in imitation of ὀπωρῑνῷ which is a metrically necessity in [Refs 8th c.BC+]