Etymology
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cloister (n.)

early 13c., cloystre, "a monastery or convent, a place of religious retirement or seclusion," from Old French cloistre "monastery, convent; enclosure" (12c., Modern French cloître), from Medieval Latin claustrum "portion of monastery closed off to laity," from Latin claustrum (usually in plural, claustra) "place shut in, enclosure; bar, bolt, means of shutting in," from past participle stem of claudere "to close, shut" (see close (v.)).

"The original purpose of cloisters was to afford a place in which the monks could take exercise and recreation" [Century Dictionary]. Spelling in French influenced by cloison "partition." Old English had clustor, clauster in the sense "prison, lock, barrier," directly from Latin, and compare, from the same source, Dutch klooster, German Kloster, Polish klasztor.

From c. 1300 in English as "covered walk running round the walls of a monastic building or large church;" from late 14c. in the general sense "colonnade round an open court." 

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cloister (v.)

"confine in a cloister or convent," c. 1400 (implied in cloistered), from cloister (n.). Figurative use, "shut up in retirement from the world," is from c. 1600. Related: Cloistered; cloistering.

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cloistral (adj.)

"of or pertaining to a cloister," c. 1600, from cloister + -al (1).

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claustration (n.)

"act of shutting up in a cloister," 1863, as if from a noun of action formed in Latin from Latin claustrare, from claustrum (see cloister).

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claustral (adj.)

mid-15c., "of or pertaining to a cloister, monastic," from Medieval Latin claustralis "pertaining to a claustrum," ("cloister"), from past participle of Latin claudere "to close" (see close (v.), and compare cloister). From 1862 as "resembling a cloister."

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*klau- 

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." 

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Satanophobia (n.)

"excessive fear of the Devil, morbid dread of Satan," 1860 ("The Cloister and the Hearth"), from Satan + -phobia, with connective -o-.

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septem- 

word-forming element meaning "seven," from Latin septem-, from septem "seven" (see seven). "The Cloister and the Hearth" (1861) has septemvious "going seven different ways" (with Latin via "way").

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carrel (n.)

1590s, "a small study in a cloister," from Medieval Latin carula "enclosure in a cloister in which to sit and read," which is of unknown origin; perhaps from Latin corolla "little crown, garland," used in various senses of "ring" (for example, in a c. 1330 description of Stonehenge: "þis Bretons renged about þe feld, þe karole of þe stones beheld"); extended to precincts and spaces enclosed by rails, etc. Specific sense of "private cubicle in a library" is from 1912.

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nunnery (n.)

late 13c., nonnerie, "nunhood, the life of nuns," from nun + -ery or from Old French nonnerie. Meaning "convent or cloister for the exclusive use of nuns" is from c. 1300. Transferred meaning "house of ill fame" is attested by 1590s.

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