Heading off trouble is not the same (5)
I believe the answer is:
other
'not the same' is the definition.
(thesaurus)
'heading off trouble' is the wordplay.
'heading off' means to remove the first letter.
'trouble' becomes 'bother' ('bother' can be a synonym of 'trouble').
'bother' with its initial letter taken off is 'OTHER'.
'is' is the link.
(Other definitions for other that I've seen before include "Not the one mentioned" , "One may be significant" , "Throe (anag)" , "not like you" , "Alternate; additional" .)