curmudgeon (n.)

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; 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.