Get on and off plan (6)
I believe the answer is:
agenda
'plan' is the definition.
(agenda is a kind of plan)
'get on and off' is the wordplay.
'get on' becomes 'age' (synonyms).
'off' indicates an anagram.
'and' is an anagram of 'nda'.
'age'+'nda'='AGENDA'
(Other definitions for agenda that I've seen before include "Meeting's topics" , "List of items to be done" , "Schedule - things to be done" , "Programme of a meeting" , "Matters to be addressed" .)