Description from Rothstein, Natalie, ed. Four Hundred Years of Fashion. London: Victoria and Albert Museum, 1984.
"Nightgown, cream flannel with black wool tufts imitating ermine ... [English] There are two pocket holes let into the side seams set close to the centre back pleat. The buttons are covered in linen. The edges trimmed with cream silk twill ... [This nightgown was originally owned by] Thomas Coutts (1735-1822), founder of Coutts Bank .... `Cossack' Trousers, unbleached linen [English] ... The trousers are cut full, tapered to the ankles, and kept taut by buttoned straps under the instep. They are attached to a deep waistband and evenly gathered at the front. `Cossack' trousers were introduced after 1814 when the Czar came to London for the peace celebrations and brought Cossack soldiers with his entourage" (149-50).
The nightgown is a type of dress men no longer have, sort of a combination of lounge wear, pajamas, and bathrobe. The fact that the nightgown is imitation ermine is interesting since men rarely wear fur today. While her husband wore such an outfit as this, a lady would probably wear morning dress.