curmudgeon n.

"churlish, miserly fellow, mean man," 1570s, of unknown origin. The suggestion, based on a misreading of a garbled note from Johnson, that it is from French coeur mechant "evil heart" is not taken seriously; nor is the notion [in Century Dictionary] that it is a corruption of corn merchant (with the notion of "one who withholds food"). The first syllable may be cur "dog." Liberman says the word "must have been borrowed from Gaelic (and references muigean "disagreeable person"), with variant spelling of intensive prefix ker-. Related: Curmudgeonly.