When one chooses a woven fabric (2,4)
I believe the answer is:
at will
'when one chooses' is the definition.
(I've seen this before)
'a woven fabric' is the wordplay.
'woven fabric' becomes 'twill' (I've seen this in another clue).
'a'+'twill'='AT WILL'
(Other definitions for at will that I've seen before include "When I choose" , "Whenever one wishes" , "take it as I please" , "when one wants" , "Fire .. .... - whenever you're ready" .)