Old English catt (c.700), from West Germanic (c.400-450), from Proto-Germanic *kattuz (cf. Old Frisian katte, Old Norse köttr, Dutch kat, Old High German kazza, German Katze), from Late Latin cattus.
The near-universal European word now, it appeared in Europe as Latin catta (Martial, c.75 C.E.), Byzantine Greek katta (c.350) and was in general use on the continent by c.700, replacing Latin feles. Probably ultimately Afro-Asiatic (cf. Nubian kadis, Berber kadiska, both meaning "cat"). Arabic qitt "tomcat" may be from the same source. Cats were domestic in Egypt from c.2000 B.C.E., but not a familiar household animal to classical Greeks and Romans. The nine lives have been proverbial since at least 1560s.
The Late Latin word also is the source of Old Irish and Gaelic cat, Welsh kath, Breton kaz, Italian gatto, Spanish gato, French chat (12c.). Independent, but ultimately from the same source are words in the Slavic group: Old Church Slavonic kotuka, kotel'a, Bulgarian kotka, Russian koška, Polish kot, along with Lithuanian kate and non-Indo-European Finnish katti, which is from Lithuanian.
Extended to lions, tigers, etc. c.1600. As a term of contempt for a woman, from early 13c. Slang sense of "prostitute" is from at least c.1400. Slang sense of "fellow, guy," is from 1920, originally in U.S. Black English; narrower sense of "jazz enthusiast" is recorded from 1931.
Cat's paw (1769, but cat's foot in the same sense, 1590s) refers to old folk tale in which the monkey tricks the cat into pawing chestnuts from a fire; the monkey gets the nuts, the cat gets a burnt paw. Cat bath "hurried or partial cleaning" is from 1953. Cat burglar is from 1907, so called for stealth. Cat-witted "small-minded, obstinate, and spiteful" (1670s) deserved to survive. For Cat's meow, cat's pajamas, see bee's knees.
1975, medical acronym for computerized axial tomography or something like it. Related: CAT scan.
computerized axial tomography
To disclose a secret: “The mayor's visit was to be kept strictly confidential, but someone must have let the cat out of the bag, because the airport was swarming with reporters.”
To reveal a secret, usually without intending to: Her guilty smile pretty much let the cat out of the bag (1760+)
A bulldozer or Caterpillar tractor
[1940s+; fr Caterpillar, trademark for a kind of continuous-track tractor]
A catamaran boat (1960s+)
A Cadillac: Tia Juana pulled up in his long green Cat (1940s+ Black)