Vegetarian not irate, perhaps, but very thoroughgoing (5)
I believe the answer is:
vegan
'very thoroughgoing' is the definition.
I can't tell whether this defines the answer.
'vegetarian not irate perhaps' is the wordplay.
'not' is a deletion indicator.
'perhaps' is an anagram indicator.
'vegetarian' with 'irate' taken out is 'vgean'.
'vgean' is an anagram of 'VEGAN'.
'but' is the link.
Can you help me to learn more?
(Other definitions for vegan that I've seen before include "One refusing animal products" , "Conscientious consumer" , "One not eating or using animal products" , "Non-consumer of animal products" , "An extreme vegetarian" .)