Seabird in water now (4)
I believe the answer is:
tern
'seabird' is the definition.
(tern is a kind of seabird)
'in water now' is the wordplay.
'in' indicates a hidden word.
'TERN' is hidden within 'water now'.
(Other definitions for tern that I've seen before include "Fork-tailed seabird" , "Rent out the bird" , "Fork-tailed relative of the gull" , "Sea bird, a small gull" , "Long-winged aquatic bird" .)