Isn't a horrible head showing spite? (9)
I believe the answer is:
nastiness
'spite?' is the definition.
(I know that spite can be written as nastiness)
'isn't a horrible head' is the wordplay.
'horrible' is an anagram indicator.
'head' becomes 'ness' (ness is a headland).
'isnt'+'a'='isnta'
'isnta' with letters rearranged gives 'nasti'.
'nasti'+'ness'='NASTINESS'
'showing' acts as a link.
(Other definitions for nastiness that I've seen before include "repugnance" , "Malevolence" , "Pollution" , "hostility" , "ill humour" .)