I'm going to start using the word "loungerie" tonight! Etymology: this ad.
I have a swell vintage velvet item that might be a dressing gown, but also might be an opera coat. I often spoil myself and wear it as a robe, but sometimes I feel bad for treating such a pretty thing so casually. And I have a terry robe that's nice after showering, but it's too bulky for lounging. So I lounge in an MHC sweatshirt or an ancient chamios shirt over PJs. Since the latter is lavender, it kinda-sorta has the feel of the swingy little robe in that ad. I would love to find a little robe like that! At the least, I can start calling a chamios shirt-over-pajamas my loungerie.