The headword is an adjective in the nominative (and vocative) feminine singular, which here presupposes the feminine noun w(/ra; cf. omicron 585, kappa 1860 (gloss), and see LSJ s.v.
Same entry, according to Adler, in the Ambrosian Lexicon (496).
[1] In the gloss, o)/rqrou is the genitive singular of the masculine noun o)/rqros. LSJ s.v. defines it as daybreak, dawn, but Wallace [below], reviewing all the evidence, insists on the dark, pre-dawn hours of night.