Green’s Dictionary of Slang

(US) a guitar; also as v.

1928		Memphis jug Band ‘She Stays Out All Night Long’ 🎵 [spoken] Now you gittfiddlin’, gitfiddle it, Will.These boys know how to do that thing.
1935		Z.N. Hurston Mules and Men (1995) 84: De git Fiddles was raisin’ cain over in de corner.
1949		L. Hughes Tambourines to Glory I vi: A little blues won’t hurt [...] you got a pretty gitfiddle, boy.
1957		M. Shulman Rally Round the Flag, Boys! (1959) 186: ‘Ah brought muh git-fiddle.’ He slung his [...] guitar aound his neck.
1969		in DARE.
1977		J. Cheever Falconer 87: I made a very big decision. I’m going to sell my gitfiddle.
1984		K. Weaver Texas Crude 113: Git-fiddle, or gitbucket. A guitar. ‘That Chet Atkins can make that gitfiddle stand up and talk.’.