An onomatopoeia for a short, sharp hissing, swishing, or whooshing sound or motion (often used as 'shuu to' or 'shuu tto').
スプレー缶を押すと『しゅー』と冷たい霧が出た。
When I pressed the spray can, a cold mist came out with a 'shuu' sound.
冬の朝、窓の隙間を風がしゅーっと吹き抜けた。
On a winter morning, the wind whooshed through the gap in the window.
蒸気が釜の隙間からしゅーっと漏れたので注意した。
Steam hissed out from a gap in the kettle, so I was careful.
子どもが遊びながら息をしゅーっと吹きかけて風船を膨らませた。
The child blew air with a 'shuu' sound while playing to inflate the balloon.