Great sin could make you most irate (8)
I believe the answer is:
angriest
'most irate' is the definition.
('angry' can be similar in meaning to 'irate')
'great sin could make you' is the wordplay.
'could make you' indicates an anagram.
'great'+'sin'='greatsin'
'greatsin' anagrammed gives 'ANGRIEST'.
(Other definitions for angriest that I've seen before include "Extremely mad" , "Most irate and furious" , "Most annoyed or hostile" , "Most characteristic of 1950s young men" , "Most wrathful" .)