A fabric that's woven when one chooses (2,4)
I believe the answer is:
at will
'when one chooses' is the definition.
(I've seen this before)
'a fabric that's woven' is the wordplay.
I cannot really understand how this works, but
'a' is found in the answer.
'fabric' could be 'twill' (type of fabric) and 'twill' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for at will that I've seen before include "Fire .. .... - whenever you're ready" , "Whenever you please, as you like" , "Freely" , "take it as I please" , "When I choose" .)