Outstanding feature primarily of cotton twill fabric (5)
I believe the answer is:
chino
'cotton twill fabric' is the definition.
(I've seen this before)
'outstanding feature primarily of' is the wordplay.
'outstanding feature' becomes 'chin' (facial feature).
'primarily' indicates taking the first letters.
The initial letter of 'of' is 'o'.
'chin'+'o'='CHINO'
(Other definitions for chino that I've seen before include "Coarse cotton khaki-coloured fabric" , "Cotton textile material" , "Twilled cotton cloth" , "strong cloth" , "Cotton cloth used in trousers" .)