Line up clothing (5)
I believe the answer is:
dress
This clue is a double definition.
'line up' is the first definition.
('dress' can be a synonym of 'line up')
'clothing' is the second definition.
(dress is a kind of clothing)
(Other definitions for dress that I've seen before include "This woman might slip on" , "get into gear" , "This circle is the first gallery in a theatre" , "Costume" , "Do some cover work in theatre" .)