Bailly
ἀκρό·νυκτος, ος, ον, c. ἀκρονύκτιος PROCL. Ptol. p. 38.
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LSJ
ον, lit.
rising at sunset; hence, in opposition, Ζεύς Vett.Val. 168.13; ἀ. σχηματισμοί, προηγήσεις, Ptol. Alm. 10.6, Tetr. 78; — as Subst., -νυκτος, ἡ, with or without φάσις, opposition, Ptol. Alm. 10.7, Tetr. 77. (Freq. written ἀκρων-.)
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)