Numerous folk etymologies exist for this word.
An alternative spelling attested in 1600 is cornmudgin, in Holland's translation of Livy, rendering frumentarius "corn-merchant". This has been suggested as the original form of the word, but OED notes that curmudgeon is attested some years before this, concluding that cornmudgin was merely a nonce-word by Holland.
The word is attested from the late 1500s in the forms curmudgeon and curmudgen, and during the 17th century in numerous spelling variants, including cormogeon, cormogion, cormoggian, cormudgeon, curmudgion, curmuggion, curmudgin, curr-mudgin, curre-megient.
curmudgeon (plural curmudgeons)
- (archaic) A miser.
- An ill-tempered (and frequently old) person full of stubborn ideas or opinions.
- There's a cranky curmudgeon working at the hospital who gives all the patients and other doctors flak.
- John Doe's old age and stubborn aversion to new ideas make him a curmudgeon of a candidate.
- 1996, Jeet Heer, Gravitas, Autumn 1996
- After a while, as cultural debates became more polarized, the editorial tone of the New Criterion went from being charmingly curmudgeon to being bitterly shrill.
- 2006, The New York Times 
- How to Be a Curmudgeon on the Internet
- 2007, The Times 
- How should I respond, without appearing to be a curmudgeon?