Genuine in nature, always (4)
I believe the answer is:
real
'genuine' is the definition.
(I know that genuine can be written as real)
'in nature always' is the wordplay.
'in' says the answer is hidden in the clue.
'REAL' is hidden in the letters of 'nature always'.
(Other definitions for real that I've seen before include "Certainly no counterfeit" , "'Genuine, actual (4)'" , "Type of ale" , "Pukka" , "foreign currency" .)