1"devil (also fiend) a (also the) haet": not a whit, nothing at all.
2"damn the haet" (formerly also "†damned haet"): nothing at all.
3Chiefly in negative contexts: a whit, a jot; the least thing; a small quantity.
Early 18th century. From hae't, misapprehended as a noun, probably after phrases like the devil a bit, the devil a whit.