Artist’s husband, impetuous (4)
I believe the answer is:
rash
'impetuous' is the definition.
(thesaurus)
'artist's husband' is the wordplay.
'artist's' becomes 'ras' (Royal Academician, member of Royal Academy of Arts).
'husband' becomes 'h'.
'ras'+'h'='RASH'
(Other definitions for rash that I've seen before include "Foolish; skin problem" , "Lacking in caution" , "Hasty; skin disorder" , "sign of irritation?" , "Impulsive - eruption" .)