Webster's Collegiate USA, 10ed, 1996, cites chomp as "alter. of champ." This change from a to o also occurs with strop (leather strap for stropping a razor) (See Mencken, The American Language). Some words have been incorrect in the eye of the beholder ever since Johnson and others tried unsuccessfully to pin English down, but they will never die. Ain't is an example. By the 1920s, Mencken reported that ain't "is already tolerably respectable in the first person, where English countenances the even more clumsy aren't" (the Appalachian am't I for am I not has now disappeared). The word shit (shite) goes back to Old English but currently is not accepted in "polite society," except in parts of Wales, etc. It is usage which determines correctness or incorrectness, and usage is constantly shifting (only slightly more stable than popularity polls).