To breathe out no longer healthy? (6)
I believe the answer is:
exhale
'to breathe out' is the definition.
('exhale' can be a synonym of 'breathe out')
'no longer healthy?' is the wordplay.
'no longer' becomes 'ex'.
'healthy?' becomes 'hale' (similar in meaning).
'ex'+'hale'='EXHALE'
(Other definitions for exhale that I've seen before include "produce emissions" , "Joint of chicken" , "send forth wind" , "expire" , "Give out" .)