The origin of the English noun 'Curmudgeon' is unknown.

It was in use as early as the 1570s, but its exact origin has apparently been lost.

The Gaelic word 'muigean' meaning a 'disagreeable person' was also in use around the same time. The 'Cur' part might have come from an old word for 'Dog'plugin-autotooltip__plain plugin-autotooltip_big'Dog' etymology

"Dog (n.) Old English docga, a late, rare word, used in at least one Middle English source in reference to a powerful breed of canine. The word forced out Old English hund (the general Germanic and Indo-European word; see canine) by 16c. and subsequently was picked up in many continental languages (French (which also has an obscure origin).

For full details, see Etymology online

Note: The Online Etymology Dictionary maintains a free-access list of the origins of thousands of English words, a significant proportion of which are unknown