c.1200, "to shut, cover in," from Old French clos- (past participle stem of clore "to shut, to cut off from"), 12c., from Latin clausus, past participle of claudere "to shut, close; to block up, make inaccessible; put an end to; shut in, enclose, confine" (always -clusus, -cludere in compounds).
The Latin word might be from the possible PIE root *klau- "hook, peg, crooked or forked branch" (used as a bar or bolt in primitive structures); cf. Latin clavis "key," clavus "nail," claustrum "bar, bolt, barrier," claustra "dam, wall, barricade, stronghold;" Greek kleidos (genitive) "bar, bolt, key," klobos "cage;" Old Irish clo "nail," Middle Irish clithar "hedge, fence;" Old Church Slavonic ključi "hook, key," ključiti "shut;" Lithuanian kliuti "to catch, be caught on," kliaudziu "check, hinder," kliuvu "clasp, hang;" Old High German sliozan "shut," German schließen "to shut," Schlüssel "key."
Also partly from Old English beclysan "close in, shut up." Intransitive sense "become shut" is from late 14c. Meaning "draw near to" is from 1520s. Intransitive meaning "draw together, come together" is from 1550s, hence the idea in military verbal phrase close ranks (mid-17c.), later with figurative extensions. Meaning "bring to an end, finish" is from c.1400; intransitive sense "come to an end" is from 1826. Of stock prices, from 1860. Meaning "bring together the parts of" (a book, etc.) is from 1560s. Related: Closed; closing.
