Job for tradesman desperately keen to secure one (8)
I believe the answer is:
painting
'job for tradesman' is the definition.
'desperately keen to secure one' is the wordplay.
'desperately keen' becomes 'panting'.
'to secure' is an insertion indicator (inserted letters are secured inside).
'one' becomes 'I' (Roman numeral).
'panting' enclosing 'i' is 'PAINTING'.
(Other definitions for painting that I've seen before include "Work of art" , "Graphic art" , "Artwork" , "picture" , "image?" .)