bedgown

An article of women's clothing for the upper body, usually worn in bed, thigh-length and wrapping or tying in front; a bedjacket.

And there sat by the empty fireplace, which was filled with a pot of sweet herbs, the nicest old woman that ever was seen, in her red petticoat, and short dimity bedgown, and clean white cap, with a black silk handkerchief over it, tied under her chin.

A nightgown.