(UK) An item of clothing often made from cotton or another absorbent material, in the form of a long open robe with a belt to tie it around the middle and fasten it securely; often worn over pyjamas.
I was feeling just as I had felt in the old Malvern House epoch when I used to sneak down to [the headmaster]'s study at dead of night in quest of the biscuits he kept there in a tin on his desk, and there came back to me the memory of the occasion when, not letting a twig snap beneath my feet, I had entered his sanctum in pyjamas and a dressing-gown, to find him seated in his chair, tucking into the biscuits himself. [...] She was looking more like Sherlock Holmes than ever. Slap a dressing-gown on her and give her a violin, and she could have walked straight into Baker Street and no questions asked.