The headword, unattested outside lexicography, is a poetic-sounding masculine noun in the nominative singular; see LSJ s.v. [In her critical apparatus, Adler noted that ms S transmits o)rqiofoi/ths, otherwise unattested.]
[1] The headword is identically glossed in the Synagoge, Photius' Lexicon (omicron474 Theodoridis), Lexica Segueriana 320.16. The glossing participle is aorist middle, masculine nominative singular, of the verb paragi/gnomai, I am present alongside, I arrive; see LSJ s.v. Here it governs o)/rqrou, genitive singular of the noun o)/rqros, -ou, o( (daybreak, dawn); see LSJ s.v.