The Saint becomes irresolute (8)
I believe the answer is:
hesitant
'irresolute' is the definition.
('hesitant' can be similar in meaning to 'irresolute')
'the saint becomes' is the wordplay.
'becomes' indicates an anagram.
'the'+'saint'='thesaint'
'thesaint' is an anagram of 'HESITANT'.
(Other definitions for hesitant that I've seen before include "Reluctant, vacillating" , "Reluctant (to speak, act)" , "Not quick" , "Undecided, halting" , "Demurring" .)