Austere boat given to saint (5)
I believe the answer is:
stark
'austere' is the definition.
(I know that austere can be written as stark)
'boat given to saint' is the wordplay.
'boat' becomes 'ark' (ark is a kind of boat).
'given to' says to put letters next to each other.
'saint' becomes 'st' (abbreviation).
'ark' after 'st' is 'STARK'.
(Other definitions for stark that I've seen before include "stern" , "Utterly" , "Absolutely crazy" , "Severe in appearance" , "Severe, bare" .)