1871, the French word for "closure, the action of closing," applied to debates in the French Assembly ("action of closing (debate) by will of a majority"), then to the House of Commons and U.S. Congress, from French clôture, from Old French closture (see closure). It was especially used in English by those opposed to the tactic.

In foreign countries the Clôture has been used notoriously to barricade up a majority against the "pestilent" criticism of a minority, and in this country every "whip" and force is employed by the majority to re-assert its continued supremacy and to keep its ranks intact whenever attacked. How this one-sided struggle to maintain solidarity can be construed into "good for all" is inexplicable in the sense uttered. ["The clôture and the Recent Debate, a Letter to Sir J. Lubbock," London, 1882]

late 14c., "a barrier, a fence," from Old French closure "enclosure; that which encloses, fastening, hedge, wall, fence," also closture "barrier, division; enclosure, hedge, fence, wall" (12c., Modern French clôture), from Late Latin clausura "lock, fortress, a closing" (source of Italian chiusura), from past participle stem of Latin claudere "to close" (see close (v.)).

Sense of "act of closing, a bringing to a close" is from early 15c. In legislation, especially "closing or stopping of debate" (compare cloture). Sense of "tendency to create ordered and satisfying wholes" is 1924, from Gestalt psychology.

also *kleu-, klēu-, Proto-Indo-European root meaning "hook, crook," also "crooked or forked branch" (used as a bar or bolt in primitive structures). 

It forms all or part of: anschluss; autoclave; clause;  claustrophobia; claves; clavichord; clavicle; clavier; claviger; clechy; clef; cloison; cloisonne; cloister; close (v.); close (adj.); closet; closure; cloture; clove (n.1) "dried flowerbud of a certain tropical tree, used as a spice;" cloy; conclave; conclude; disclose; enclave; enclose; exclude; foreclose; include; occlude; preclude; recluse; seclude; slot (n.2) "bar or bolt used to fasten a door, window, etc." 

It is the hypothetical source of/evidence for its existence is provided by: Greek kleis "bar, bolt, key; collarbone," klobos "cage;" Latin clavis "key," clavus "nail," claudere "to shut, close;" Lithuanian kliūti "to catch, be caught on," kliaudžiu, kliausti "to check, hinder," kliūvu, kliūti "to clasp, hang;" Old Church Slavonic ključi "hook, key," ključiti "shut;" Old Irish clo "nail," Middle Irish clithar "hedge, fence;" Old High German sliozan "shut," German schließen "to shut," Schlüssel "key."