I rave in a bad temper (5)
I believe the answer is:
irate
'i' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?
'rave in a bad temper' is the wordplay.
'rave' becomes 'at' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'a bad temper' becomes 'ire' (I've seen this in another clue).
'at' put inside 'ire' is 'IRATE'.
Can you help me to learn more?
(Other definitions for irate that I've seen before include "Angry and incensed" , "ranting" , "Hacked off" , "Infuriated" , "Wrathful" .)