Always in perseverance (4)
I believe the answer is:
ever
'always' is the definition.
(synonyms)
'in perseverance' is the wordplay.
'in' says the answer is hidden in the clue.
'EVER' is hidden within 'perseverance'.
(Other definitions for ever that I've seen before include "Continuously" , "To the end of time" , "Veer away endlessly" , "constantly" , "Possibly" .)