Convert polyester for weaving (9)
I believe the answer is:
proselyte
'convert' is the definition.
(term for a religious convert)
'polyester for weaving' is the wordplay.
'for weaving' indicates anagramming the letters (letters weaved or shaped).
'polyester' is an anagram of 'PROSELYTE'.
(Other definitions for proselyte that I've seen before include "Convert to a religion, particularly Jewish" , "recruit" , "Religious convert" , "One now thinks differently" .)