The Collaborative International Dictionary of English v.0.48:
Hebdomad \Heb"do*mad\, n. [L. hebdomas, -adis, Gr. "ebdoma`s the number seven days, fr. ? seventh, ? seven. See Seven.] A week; a period of seven days. [R.] --Sir T. Browne. HebdomadalWordNet (r) 3.0 (2006):
hebdomad n 1: any period of seven consecutive days; "it rained for a week" [syn: week, hebdomad]