Eg Hammerstein's very big estate, perhaps (5)
I believe the answer is:
oscar
'eg hammerstein's' is the definition.
(lyricist Oscar Hammerstein)
'big estate perhaps' is the wordplay.
'big' becomes 'os'.
'estate perhaps' becomes 'car' (estate is a type of car).
'os'+'car'='OSCAR'
'very' acts as a link.
(Other definitions for oscar that I've seen before include "Note" , "Statuette awarded by Hollywood Academy" , "Title of Hollywood Academy award" , "Film statuette" , "-- Wilde, author" .)