Eccentric nut getting spiteful was not intended (7)
I believe the answer is:
unmeant
'not intended' is the definition.
(I've seen this in another clue)
'eccentric nut getting spiteful' is the wordplay.
'eccentric' indicates anagramming the letters.
'getting' indicates putting letters inside.
'spiteful' becomes 'mean' (synonyms).
'nut' is an anagram of 'unt'.
'unt' placed around 'mean' is 'UNMEANT'.
'was' acts as a link.
(Other definitions for unmeant that I've seen before include "accident" , "Accidental" , "not intended" .)