frail eel, n. — Green’s Dictionary of Slang

frail eel n.

[frail n.¹ (2) + SE eel, an elusive creature which is hard to hold on to; ? poss. Zora-Neale Hurston nonce-word]

(US black) an attractive woman.

1933		Z.N. Hurston Gilded Six-Bits (1995) 987: Y’all pritty lil frail eels don’t ned nothin’ lak dis. You too sweet already.
1935		Z.N. Hurston Mules and Men (1995) 169: All dese frail eels gittin’ skittish.
1942		Z.N. Hurston ‘Story in Harlem Sl.’ in Novels and Stories (1995) 1001: Whenever he was challenged by a hard-head or a frail eel on the right of his title he would eye-ball the idol-breaker with a slice of ice.