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clause [clause 词源字典]: clause: [13] The etymological notion underlying clause is of ‘closing’ or ‘termination’. The word derives ultimately from Latin claudere (source of English close) and was originally applied either as a rhetorical term to the conclusion of a sentence, or as a legal term to the termination of a legal argument. Gradually, in both cases, the element of finality fell away, leaving the senses ‘short sentence’ and ‘section of a legal document’, which passed into English.

The past participle of Latin claudere, clausus, probably produced an unrecorded noun *clausa (known only in its diminutive form clausula), which passed into English via Old French clause.
=> clavier, close[clause etymology, clause origin, 英语词源]
claustrophobia: claustrophobia: see cloister
clausal (adj.): 1870, from clause + -al (1).
clause (n.): c. 1200, "a sentence, a brief statement, a short passage," from Old French clause "stipulation" (in a legal document), 12c., from Medieval Latin clausa "conclusion," used in the sense of classical Latin clausula "the end, a closing, termination," also "end of a sentence or a legal argument," from clausa, fem. noun from past participle of claudere "to close, to shut, to conclude" (see close (v.)). Grammatical sense is from c. 1300. Legal meaning "distinct condition, stipulation, or proviso" is recorded from late 14c. in English. The sense of "ending" seems to have fallen from the word between Latin and French.
claustral (adj.): "resembling a cloister," early 15c., from Middle French claustral (15c.) and directly from Medieval Latin claustralis "pertaining to a claustrum" (see cloister).
claustration (n.): 1863, "act of shutting up in a cloister," as if from a noun of action formed in Latin from Latin claustrare, from claustrum (see cloister).
claustrophilia (n.): "morbid desire to be shut up in a confined space," 1884, from claustro-, abstracted from claustrophobia, + -philia.
claustrophobia (n.): "morbid fear of being shut up in a confined space," coined 1879 (in article by Italian-born, French-naturalized Swiss-English physician Dr. Benjamin Ball (1834-1892)) from Latin claustrum "a bolt, a means of closing; a place shut in, confined place, frontier fortress" (in Medieval Latin "cloister"), past participle of claudere "to close" (see close (v.)) + -phobia "fear."
claustrophobic (adj.): 1889, from claustrophobia + -ic. As a noun, "person who has claustrophobia," it is recorded from 1953.
Santa Claus (n.): 1773 (as St. A Claus, in "New York Gazette"), American English, from dialectal Dutch Sante Klaas, from Middle Dutch Sinter Niklaas "Saint Nicholas," bishop of Asia Minor who became a patron saint for children. Now a worldwide phenomenon (Japanese santakurosu). Father Christmas is attested from 1650s.