peevish

The adjective is derived from Late Middle English pievish, peuysche, pevish, pevysh (“capricious, wilful; perverse, wayward”); further etymology uncertain, possibly from one of the following:

From an unattested Old French word, from Latin perversus (“corrupted, perverted, subverted; overthrown”), the perfect passive participle of pervertō (“to corrupt, subvert; to overthrow”), from per- (prefix meaning ‘intensively, thoroughly’) + vertō (“to turn; to turn upside down, overturn, overthrow, subvert”) (ultimately from Proto-Indo-European *wert- (“to rotate; to turn”)). However, the Oxford English Dictionary says this derivation “presents some formal difficulties”.

From Middle French *expaive + -ish (similar to; somewhat, rather). *Expaive is an unattested variant of Middle French espave, Old French espave (“(adjective) of an animal: stray; of a person: foreign; (noun) flotsam; lost property”) (referring to the behaviour of stray animals; modern French épave), from Latin expavidus (“extremely frightened or horrified”), from ex- (intensifying prefix) + pavidus (“fearful, terrified; quaking, trembling; shy, timid”) (from paveō (“to be afraid; fear; to quake or tremble with fear”) (ultimately from Proto-Indo-European *paw- (“to hit, strike”)) + -idus (suffix meaning ‘tending to’ forming adjectives)).

The adverb is derived from the adjective.