Veronica's peed off? Great! (5)
I believe the answer is:
swell
'great' is the definition.
(I know that great can be written as swell)
'veronica's peed off?' is the wordplay.
'veronica' becomes 'speedwell' (speedwell can mean a veronica plant).
'off?' is a deletion indicator (some letters taken off).
'speedwell' with 'peed' taken out is 'SWELL'.
(Other definitions for swell that I've seen before include "Puff up" , "A puffed-up" , "Informally good, grow larger" , "Become larger in size" , "First class" .)