Wildly rash, hot-headed and cruel (5)
I believe the answer is:
harsh
'cruel' is the definition.
(synonyms)
'wildly rash hot-headed' is the wordplay.
'wildly' is an anagram indicator.
'hot-headed' becomes 'h' (this might be a standard abbreviation which I don't know about).
'rash' anagrammed gives 'hars'.
'hars'+'h'='HARSH'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for harsh that I've seen before include "Not relenting" , "Guttural" , "Strident" , "Raucous - austere - bitter" , "Jarring" .)