Nightshirt
/ˈnaɪtʃɜːrt/
Definition 1 of 1
Pro Tip 1/3Bedtime Clothing
A nightshirt is specifically worn for sleeping, not for daytime wear or outdoor activities. 
After his evening bath, he changed into his nightshirt.
Pro Tip 2/3Not Outerwear
Unlike regular shirts, a nightshirt is generally not appropriate to wear outside of the home. 
She realized it was too late to go shopping in her nightshirt.
Pro Tip 3/3Unisex Garment
Nightshirts can be worn by any gender, though styles may vary. 
Both the husband and wife had matching cotton nightshirts.