A garment to get perfectly straight (5)

I believe the answer is:

dress

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'a garment' is the definition.
(I know that garment can be written as dress)

I can't explain the rest of the clue.

(Other definitions for dress that I've seen before include "This circle is the first gallery in a theatre" , "formal wear" , "(Article of) clothing" , "Adorn" , "formal attire" .)

I've seen this clue in the Evening Standard.

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