LSJ
εως, ἡ, Astron., a simultaneous relation of centres, i.e. when the sun΄s centre is at that point of the ecliptic which rises, sets, or culminates coincidently with the rising, etc., of a given star, Ptol. Alm. 8.5 (pl.).
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)