"characterized by odd fancies, eccentric in thought," 1825, from crotchet "whim or fancy" + -y (2). Related: Crotchetiness. *Crotchetily seems little used, but it is an ugly word.
Entries linking to crotchety
crotchet n.
early 14c., "small hook;" mid-15c. "a staff with a hook at the end," from Old French crochet (pronounced "crotchet") "small hook; canine tooth" (12c.), diminutive of croc "hook," from Old Norse krokr "hook," which is of obscure origin but perhaps related to the widespread group of Germanic kr- words meaning "bent, hooked."
As a curved surgical instrument with a sharp hook, from 1750. Figurative use in musical notation for "quarter note" is from mid-15c., from the shape of the notes. Also from 1670s in now-obsolete sense "one of the pair of marks now called 'brackets.'"
Meaning "whimsical fancy, singular opinion," especially one held by someone who has no competency to form a sound one, is from 1570s; the sense is uncertain, perhaps it is the same mechanical image in extended senses of crank; but other authorities link it to the musical notation one (think: "too many notes").
-y 2
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy). Adjectives such as hugy, vasty are artificial words that exist for the sake of poetical metrics.