Green’s Dictionary of Slang

(US black) a trad. plantation slave pocket knife.

1935		Z.N. Hurston Mules and Men (1995) 171: Ah could give you a knife to tote [...] Ah got two round here. One real good one Ah got down in Tampa, and one ole froe.
1947		K. Lumpkin Making of a Southerner 34: It was a large wooden building, its walls made of rough-hewn boards, [...] riven out by the slaves’ hands with a ‘fro’.