noun
A loose dress-like garment worn for sleeping, typically by women. The Japanese loanword ナイトガウン is used similarly to the English 'nightgown'.
彼女は新しいナイトガウンを着て寝た。
She slept in her new nightgown.
寝間着 is a general native Japanese term for sleepwear, including both nightgowns and pajamas.
Loanword from English 'nightgown'.