What is the X in X-mas?
early 13c., "store room," from Anglo-French celer, Old French celier "cellar, underground passage" (12c., Modern French cellier), from Latin cellarium "pantry, storeroom," literally "group of cells;" which is either directly from cella (see cell), or from noun use of neuter of adjective cellarius "pertaining to a storeroom," from cella. The sense in late Middle English gradually shifted to "underground room." Cellar door attested by 1640s.
a subterranean vault (1 Chr. 27:28), a storehouse. The word is also used to denote the treasury of the temple (1 Kings 7:51) and of the king (14:26). The Hebrew word is rendered "garner" in Joel 1:17, and "armoury" in Jer. 50:25.