Etymology: Derivation unknown.
The occurrence in Holland’s Livy, 1600, of cornmudgin n. (q.v.) has led to a suggestion that this was the original form, with the meaning ‘concealer or hoarder of corn’, mudgin being associated with Middle English much-en, mich-en to pilfer, steal, or muchier, Norman form of Old French mucier, musser to conceal, hide away. But examination of the evidence shows that curmudgeon was in use a quarter of a century before Holland’s date, and that cornmudgin is apparently merely a nonce-word of Holland’s, a play upon corn and curmudgeon. The suggestion that the first syllable is cur, the dog, is perhaps worthy of note; but that of Dr. Johnson’s ‘unknown correspondent’, cœur méchant for French méchant cœur, ‘evil or malicious heart’, is noticeable only as an ingenious specimen of pre-scientific ‘etymology’, and as having been retailed by Ash in the form, ‘from the French cœur unknown, and mechant a correspondent’!
Can anyone throw more light on the etymology?