An advantage when on TV (5)
I believe the answer is:
asset
'an advantage' is the definition.
(thesaurus)
'when on tv' is the wordplay.
'when' becomes 'as'.
'on' means one lot of letters go next to another.
'tv' becomes 'set' (I've seen this in other clues).
'as'+'set'='ASSET'
(Other definitions for asset that I've seen before include "Something that's worth having" , "Useful or valuable property" , "Anything considered valuable" , "Beneficial thing" , "Valuable possession, worth having" .)