All Geisha wear kimono, sometimes known as a Hikizuri Kimono.
The Obi is what the geisha sash is called.
Geisha wear elaborate, beautiful, and expensive silk kimono.
It is a traditional dress. Perhaps in films you have seen Geisha wearing Kimono. It was Geisha who made Kimono such a popular dress at one time. Kimono is beautiful and Japanese culture is built around asethetics.
A Kimono is the traditional apparel of Japan for both men and women. Geisha wear very beautiful elaborate kimono. It always matches with the time of the year, season, and occasion.
Geisha dress in very expensive, specially designed, silk Kimono.
To simplify Geisha wear beautiful and elaborate kimono made of expensive silk, an obi, (plus many under-kimono ties and layers), tabi sock, zori or oboko shoes, and hair kanzashi. What a Geisha wears depends very much on the month and event. She has certain kimono and certain kanzashi that she will only wear during designated months or days.
A samurai's robe is called a kimono
Kimono
Traditional Geisha always wear their hair in a traditional styled updo, or wig. And carefully planned kanzashi (hair accessories) and kimono. Their kimono, obi, and kanzashi will always match the season, and event in which they are to attend. In the link below you can see photos of a traditional Geisha.
Because everybody wore kimono during that time period.
The clothing a samurai wore outside of battle was known as the kimono.