1640s, "during, in the process of, for the time of the continuance of," a preposition formed on the model of French pendant "during," literally "hanging," present participle of pendere "to hang, cause to hang" (from PIE root *(s)pen- "to draw, stretch, spin").
The meaning is patterned on "not decided" as a secondary sense of Latin pendente (literally "hanging") in the legal phrase pendente lite "while the suit is pending, during the litigation" (with the ablative singular of lis "suit, quarrel"). The use of the present participle before nouns caused it to be regarded as a preposition. As an adjective from 1797.
1570s, "character on a staff to indicate its name and pitch," so that the others may be known, from French clef (12c.) "key; musical clef; trigger," from a figurative or transferred use of classical Latin clavis, which had only the literally sense "key" (from PIE root *klau- "hook").
In the Middle Ages, the Latin word was used in the Guidonian system for "the lowest note of a scale," which is its basis (see keynote). The most common is the treble, violin, or G-clef, which crosses on the second line of the staff, denoting that as the G above middle C on the piano.
computer language, 1964, initialism (acronym) for Beginners' All-purpose Symbolic Instruction Code; invented by Hungarian-born U.S. computer scientist John G. Kemeny and U.S. computer scientist Thomas E. Kurtz.