The Chinese word for nightie is
睡衣

shuì yī

Chinese Definition

nightie
1. 睡衣
Components
睡
1. (intransitive) to sleep
睡會huǐ兒r - to sleep for a while -
2. (of bed, room, transitive) to sleep; to have the capacity for
我睡這間房。 - I sleep in this room.
3. (colloquial, transitive) to sleep with (have sexual intercourse with somebody)
被睡了 - to be slept with (to have sexual intercourse unconsciously, unwillingly or unhappily) -
4. (dialectal) to lie; to recline
5. (literary, intransitive) to nod off
衣
1. (upper) garment; clothes; clothing
衣服 - clothes
內衣 - underwear
睡衣 - night clothes; pajamas
2. coating; covering; skin
糖衣 - sugar coating
槍衣 - gun cover
3. membrane; film
4. (literary or dialectal) afterbirth; placenta
衣yì錦還huán鄉 - to return home in glory