Learner's definition of GOWN
a long, formal dress that a woman wears especially during a special event
The bride wore a lovely lace wedding gown.
a red evening gown [=a gown that is worn to events in the evening]
a beautiful ball gown [=a gown that is worn to large formal parties for dancing]
a loose piece of clothing that is worn over other clothes during an official event by a judge, a priest, a student, etc.