Pooh
natural exclamation: first recorded in English in the late 16th century.
wiktionary
Originally onomatopoeic for a puff of air, after earlier poh and similar to later pew, phew, pho, phoo, poof. Later influenced by poop, onomatopoeic for the sound of flatulating and defecating, and by interjections of disgust similar to phew, pee-ew. Interjection for an unpleasant smell possibly linked to French puer(“to stink”).
etymonline
pooh
1590s, "a 'vocal gesture' expressing the action of puffing anything away" [OED], used as an exclamation of dislike, scorn, or contempt, first attested in Hamlet Act I, Scene III, where Polonius addresses Ophelia with, "Affection! pooh! you speak like a green girl, / Unsifted in such perilous circumstance. / Do you believe his tenders, as you call them?" But the "vocal gesture" is perhaps ancient.
