Angry, that is, about traitor (5)
I believe the answer is:
irate
'angry' is the definition.
(irate can mean angry or annoyed)
'that is about traitor' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'about' means one lot of letters goes inside another.
'traitor' becomes 'rat' (rat can mean a traitor).
'ie' going around 'rat' is 'IRATE'.
(Other definitions for irate that I've seen before include "ranting" , "Infuriated" , "Ticked off" , "Boiling" , "Extremely angry" .)