Could be mad with rage - or love (6)
I believe the answer is:
admire
'love' is the definition.
(thesaurus)
'could be mad with rage' is the wordplay.
'could be' is an anagram indicator.
'with' says to put letters next to each other.
'rage' becomes 'ire' (ire is intense rage).
'mad' is an anagram of 'adm'.
'adm'+'ire'='ADMIRE'
'or' acts as a link.
(Other definitions for admire that I've seen before include "Regard approvingly" , "Have high regard for, think well of" , "Respect greatly" , "Idolise" , "Look at (someone or something) with pleasure" .)