Part of girdle a seamstress let out (5)
I believe the answer is:
lease
'let out' is the definition.
(I've seen this before)
'part of girdle a seamstress' is the wordplay.
'part of' says the answer is hidden in the clue.
'LEASE' is hidden within 'girdle a seamstress'.
(Other definitions for lease that I've seen before include "Let; rent" , "Summer's has too short a date (Shak.)" , "Ghost" , "Term of a rental contract" , "Rent -- easel (anag)" .)