Reflexive pronoun is left out (6)
I believe the answer is:
itself
'reflexive pronoun' is the definition.
(reflexive pronoun form of 'it')
'is left out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'is'+'left'='isleft'
'isleft' is an anagram of 'ITSELF'.
(Other definitions for itself that I've seen before include "That's it, emphatically" , "See 1" , "The thing in question" , "Reflexive word - stifle (anag)" , "that's the thing" .)