Lewis Short
hebdŏmas (noun F) : ἑβδομάς
* The number seven, seven days: libri, qui inscribuntur Hebdomades,Gell. 3, 10, 1: septima fere hebdomade, id est, nono et quadragesimo die, Varr. ib. § 7: hebdomadibus lunae,on every seventh day of the moon,Gell. 15, 2, 3.—Of the critical seventh day in diseases: symphoniam Lysonis vellem vitasses, ne in quartam hebdomada incideres, Cic. Fam. 16, 9, 3 (cf. collat. form hebdomada, s. v.).
Charlton T. Lewis, Charles Short, A Latin Dictionary