adverb, adverb taking the 'to' particle
with a slap; with a splash; with a bang; flatly
Onomatopoeic adverb describing a sharp, decisive sound or action: a slap, splash, door slamming shut, or a flat refusal. Often used with と.
彼は机をぴしゃりと叩いた。
He slapped the desk with a sharp sound.
ドアがぴしゃりと閉まった。
The door banged shut.
She flatly refused the offer.