a popular pet form of the masc. proper name James (in Middle English records, Gemme, Jemme are more common than Jimme). In mid-18c. often associated with effeminacy and male fastidiousness; hence jemmy (adj.) "spruce, neat" (1750), jemminess (1756). As "a short crowbar," favored by burglars, from 1811. Compare jimmy (n.).
late 14c., jakke "a mechanical device," from the masc. name Jack. The proper name was used in Middle English for "any common fellow," and thereafter extended to various appliances which do the work of common servants (1570s). Also used generically of male animals (1620s, see jackass, jackdaw, etc.).
As a portable contrivance for raising weight by force from below, 1703. As the name of a device for pulling off boots from 1670s. The jack in a pack of playing cards (1670s) is in German Bauer "peasant." Slang meaning "money" is by 1890 (in earlier slang it meant "a small coin"). Jack-towel, one sewn together at the ends round a roller, is from 1795. The jack of Union Jack is a nautical term for "small flag at the bow of a ship" (1630s) and perhaps is from the word's secondary sense of "smaller than normal size."
"club," 1848, American English, originally burglars' slang for "crowbar;" meaning "policeman's club" first recorded 1856, probably from nickname of William, applied to various objects (compare jack, jimmy, jenny). But compare French bille "a short, stout stick" (see billet (n.1)). Billy-goat as a familiar name for a male goat is from 1826.
<a href="https://www.etymonline.com/word/jimmy">Etymology of jimmy by etymonline</a>
Harper, D. (n.d.). Etymology of jimmy. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/jimmy