Abusive to a hothead, madly rash (5)
I believe the answer is:
harsh
'abusive' is the definition.
(thesaurus)
'a hothead madly rash' is the wordplay.
'a hothead' becomes 'h' (head letter of 'hot').
'madly' indicates anagramming the letters.
'rash' with letters rearranged gives 'arsh'.
'h'+'arsh'='HARSH'
'to' is the link.
(Other definitions for harsh that I've seen before include "Rough and disagreeable, maybe of voice" , "Jarring" , "Unpleasantly stern" , "'Severe, rough (5)'" , "Abrasive, rough or unkind" .)