Describe old man wearing shirt? (5)
I believe the answer is:
paint
'describe' is the definition.
(thesaurus)
'old man wearing shirt?' is the wordplay.
'old man' becomes 'pa' (both can mean father).
'wearing' becomes 'in' (wear in (and 'in' is fashionable)).
'shirt?' becomes 't' (as in a T-shirt).
'pa'+'in'+'t'='PAINT'
(Other definitions for paint that I've seen before include "Pigment" , "Colouring matter for decoration" , "Artist's material" , "Coloured liquid in tins" , "Coloured coating" .)