Ecstatic, heading off madly to make plans (7)
I believe the answer is:
tactics
'plans' is the definition.
(tactic is a kind of plan)
'ecstatic heading off madly' is the wordplay.
'heading off' means to remove the first letter.
'madly' indicates an anagram.
'ecstatic' with its initial letter taken off is 'cstatic'.
'cstatic' is an anagram of 'TACTICS'.
'to make' is the link.
(Other definitions for tactics that I've seen before include "Art of organising battle" , "Military science" , "Ploys" , "The means adopted to achieve an end" , "Skill of using available means to reach an end" .)