une robe
a cocktail gown is 'une robe de cocktail' in French
A wedding gown is 'une robe de mariée' in French.
The word sought may be negligee (nightie, dressing gown) from the French (négligé).(The similar word is negligence, culpable neglect.)
The Japanese word Wedding Gown is ウェディングドレス.
Yes, that is one meaning of the word 'gown'.
Middle English: from Old French, from late Latin camisia'shirt or nightgown.'
She donned a gown of flowing silk.
une robe (fem.)
Gown is one syllable, so say it just like it looks.
Fedora, French Gown
It's "Robe de Bal".
une chemise de nuit