Regret is genuine after losing time (3)
I believe the answer is:
rue
'regret' is the definition.
(to rue something is to regret it)
'genuine after losing time' is the wordplay.
'genuine' becomes 'true' (synonyms).
'after losing' indicates named letters should be taken away.
'time' becomes 't' (abbreviation).
'true' with 't' removed is 'RUE'.
'is' is the link.
(Other definitions for rue that I've seen before include "Bemoan" , "Repentant sort of shrub?" , "Bitter-tasting herb" , "Regret - wild shrub" , "Be regretful" .)