dressing room
US /ˈdres.ɪŋ ˌruːm/
UK /ˈdres.ɪŋ ˌruːm/

1.
a room where actors or other performers get ready for a performance, including changing clothes and applying makeup
:
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The actress was in her dressing room preparing for the show.
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After the concert, the band relaxed in the dressing room.
2.
a room or area in a store where customers can try on clothes before buying them
:
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Please use the dressing room to try on the shirt.
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There was a long line for the dressing room during the sale.