Apparition, one gripped by violent anger (6)
I believe the answer is:
wraith
'apparition' is the definition.
(wraith is a kind of apparition)
'one gripped by violent anger' is the wordplay.
'one' becomes 'i' (Roman numeral).
'gripped by' is an insertion indicator.
'violent anger' becomes 'wrath' (I've seen this before).
'i' inserted within 'wrath' is 'WRAITH'.
(Other definitions for wraith that I've seen before include "Ghost or spectral appartition" , "Ghost-like apparition" , "looking pale and thin" , "Apparition, phantom, spirit" , "Deathly apparition" .)