Day wearing silk (5)
I believe the answer is:
satin
'silk' is the definition.
(I've seen this before)
'day wearing' is the wordplay.
'day' becomes 'sat' (short for Saturday).
'wearing' becomes 'in' (as in being 'in' certain clothes).
'sat'+'in'='SATIN'
(Other definitions for satin that I've seen before include "Rich cloth" , "covered with?" , "Stain on silky cloth" , "Stain on shiny cloth" , "Silky material" .)