Infuriate me ultimately: anger stirred up (6)
I believe the answer is:
enrage
'infuriate' is the definition.
(I've seen this before)
'me ultimately anger stirred up' is the wordplay.
'ultimately' indicates one should take the final letters.
'stirred up' is an anagram indicator.
The last letter of 'me' is 'e'.
'anger' is an anagram of 'nrage'.
'e'+'nrage'='ENRAGE'
(Other definitions for enrage that I've seen before include "Greatly anger" , "Make someone extremely angry" , "Incense" , "put people's back up" , "Make violently angry" .)