the.com/nightdress
A dress that does no work, attends no party, and answers only to bedtime.
means A loose, comfortable garment worn by women and children for sleeping.
from Plain Old English logic stitched together: night plus dress, attested since the 1700s, when sleeping in your day clothes finally fell out of fashion.
Older cousinNightgown predates it by two centuries.
Class signalOnce a luxury; many simply slept nude or in shifts.
ShrinkageModern versions traded floor-length modesty for the slip.