Still in the seventies (4)
I believe the answer is:
'still' is the definition.
(I know that still can be written as even)
'in the seventies' is the wordplay.
'in' indicates a hidden word.
'EVEN' is hidden within 'seventies'.
(Other definitions for even that I've seen before include "Plumb" , "Regular - smooth" , "Flat, smooth and divisible by two" , "Still - flat" , "no-win situation?" .)