Saint, not well yet (5)
I believe the answer is:
still
'yet' is the definition.
(I know that yet can be written as still)
'saint not well' is the wordplay.
'saint' becomes 'st' (abbreviation).
'not well' becomes 'ill' ('ill' is the opposite to 'well').
'st'+'ill'='STILL'
(Other definitions for still that I've seen before include "... [STRONG LIQUOR] produced by this" , "Yet; not moving" , "Calm - even so" , "subdued" , "not bubbly" .)