Spirit, one in anger (6)
I believe the answer is:
wraith
'spirit' is the definition.
(I've seen this before)
'one in anger' is the wordplay.
I cannot really see how this works, but
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
'anger' could be 'wrath' (wrath is a kind of anger) and 'wrath' is found within the remaining letters.
No letters remain.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for wraith that I've seen before include "Ghost or spectral appartition" , "Presence" , "Spook" , "'Ghost, spectre (6)'" , "Ghostly figure" .)