IPA: //ˈnaɪtʃɜːrt//
KK: /naɪtʃɜrt/
A long, loose piece of clothing that is worn in bed, similar to a shirt.
He put on his nightshirt before going to sleep.
Nightshirt → It is formed from "night" (from Old English *niht*, meaning the period of darkness) and "shirt" (from Old English *scyrte*, meaning a garment worn on the upper body). The word "nightshirt" refers to a garment worn during the night, typically for sleeping.
Think of the time of day when it is dark ('night') and the type of clothing you wear ('shirt') — a nightshirt is simply a shirt for wearing at night.