Plan for putting on weight (9)
I believe the answer is:
programme
'plan' is the definition.
(synonyms)
'for putting on weight' is the wordplay.
'for' becomes 'pro' (I've seen this before).
'putting on' is a charade indicator (letters next to each other).
'weight' becomes 'gramme' (I have seen 'Small weight ' mean 'gramme' so perhaps 'weight' could also mean 'gramme').
'pro'+'gramme'='PROGRAMME'
(Other definitions for programme that I've seen before include "Radio or TV show" , "Radio or TV broadcast" , "Scheduled plan" , "Schedule of proceedings" , "Radio or television show" .)