Mistakenly call the spiteful person? (7)
I believe the answer is:
hellcat
'spiteful person?' is the definition.
(I've seen this before)
'mistakenly call the' is the wordplay.
'mistakenly' indicates an anagram.
'call'+'the'='callthe'
'callthe' is an anagram of 'HELLCAT'.
(Other definitions for hellcat that I've seen before include "Unpleasant female" , "Malignant hag" , "Spiteful person" , "she-devil" , "Spiteful woman" .)