I sell new thread (5)
I believe the answer is:
lisle
'thread' is the definition.
(I know that lisle is a type of cotton)
'i sell new' is the wordplay.
'new' is an anagram indicator.
'i'+'sell'='isell'
'isell' is an anagram of 'LISLE'.
(Other definitions for lisle that I've seen before include "Fine cotton thread used in stockings" , "Strong cotton material" , "Pedestrianised city" , "Type of cotton yarn" , "(Fabric woven with) a fine cotton thread" .)