What is the X in X-mas?
early 12c., "small monastery, subordinate monastery" (from Medieval Latin in this sense), later "small room for a monk or a nun in a monastic establishment; a hermit's dwelling" (c.1300), from Latin cella "small room, store room, hut," related to Latin celare "to hide, conceal."
The Latin word represents PIE root *kel- "conceal" (cf. Sanskrit cala "hut, house, hall;" Greek kalia "hut, nest," kalyptein "to cover," koleon "sheath," kelyphos "shell, husk;" Latin clam "secret;" Old Irish cuile "cellar," celim "hide," Middle Irish cul "defense, shelter;" Gothic hulistr "covering," Old English heolstor "lurking-hole, cave, covering," Gothic huljan "cover over," hulundi "hole," hilms "helmet," halja "hell," Old English hol "cave," holu "husk, pod").
Sense of monastic rooms extended to prison rooms (1722). Used in 14c., figuratively, of brain "compartments;" used in biology by 17c. of various cavities (e.g. wood structure, segments of fruit, bee combs), gradually focusing to the modern sense of "basic structure of living organisms" (which OED dates to 1845).
Electric battery sense is from 1828, based on original form. Meaning "small group of people working within a larger organization" is from 1925. Cell body is from 1851; cell division from 1846; cell membrane from 1837 (but cellular membrane is 1732); cell wall from 1842.
The smallest structural unit of an organism that is capable of independent functioning, consisting of one or more nuclei, cytoplasm, and various organelles, all surrounded by a semipermeable cell membrane.
A small enclosed cavity or space.
A region of the atmosphere in which air tends to circulate without flowing outward.