clauseyoudaoicibaDictYouDict[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]
clause (n.)youdaoicibaDictYouDict
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.