Sab·bath 
(săbəth)
(săbəth)n.
1. The seventh day of the week, Saturday, observed as the day of rest and worship in Judaism and some Christian sects.
2. The first day of the week, Sunday, observed as the day of rest and worship in most forms of Christianity.
[Middle English sabat, from Old French sabbat and Old English sabat, both from Latin sabbatum, from Greek sabbaton, from Hebrew šabbāt, from šābat, to cease, rest; see šbt in the Appendix of Semitic roots.]