Brussels

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" (from PIE root *kel- (1) "to cover, conceal, save").

From "monastic room" the sense was extended to "prison room" (1722). The word was used in 14c., figuratively, of brain "compartments" as the abode of some faculty; it was used in biology by 17c. of various cavities (wood structure, segments of fruit, bee combs), gradually focusing to the modern sense of "basic structure of all living organisms" (which OED dates to 1845).

Electric battery sense is from 1828, based on the "compartments" in very early types. The 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 (cellular membrane is by 1732), cell wall is attested from 1842.

Proto-Indo-European root meaning "to cover, conceal, save."

It forms all or part of: Anselm; apocalypse; Brussels; caliology; Calypso; calyx; ceiling; cell; cellar; cellular; cellulite; cellulitis; cilia; clandestine; cojones; coleoptera; color; conceal; eucalyptus; hall; hell; helm (n.2) "a helmet;" helmet; hold (n.2) "space in a ship below the lower deck;" hole; hollow; holster; housing (n.2) "ornamental covering;" hull (n.1) "seed covering;" kil-; kleptomania; occult; rathskeller; supercilious; Valhalla; William.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit cala "hut, house, hall;" Greek kalia "hut, nest," kalyptein "to cover," koleon, koleos "sheath," kelyphos "shell, husk;" Latin cella "small room, store room, hut," celare "to hide, conceal," clam "secret," clepere "to steal, listen secretly to;" Old Irish cuile "cellar," celim "hide," Middle Irish cul "defense, shelter;" Gothic hulistr "covering," Old English heolstor "lurking-hole, cave, covering," Gothic huljan "to cover over," hulundi "hole," hilms "helmet," halja "hell," Old English hol "cave," holu "husk, pod;" Old Prussian au-klipts "hidden;" Old Church Slavonic poklopu "cover, wrapping."