Right to enter complaint in dispute (5)
I believe the answer is:
argue
'dispute' is the definition.
(thesaurus)
'right to enter complaint' is the wordplay.
'right' becomes 'r' (common abbreviation).
'to enter' is an insertion indicator.
'complaint' becomes 'ague' (ague is a kind of disease**).
'r' inserted within 'ague' is 'ARGUE'.
'in' acts as a link.
(Other definitions for argue that I've seen before include "Dispute heatedly" , "Disagree violently" , "Disagree heatedly" , "Discuss, contend" , "Fabric hanging in folds" .)