Set on rising (3)
I believe the answer is:
gel
'set' is the definition.
(both can mean to harden)
'on rising' is the wordplay.
'on' becomes 'leg' (cricket term).
'rising' shows that the letters should be reversed in order (in a down clue, letters go up).
'leg' written backwards gives 'GEL'.
(Other definitions for gel that I've seen before include "Capital preparation" , "posh lass" , "Mousse" , "Hair treatment" , "Congeal - hair dressing" .)