Rowers had dinner, we hear (5)
I believe the answer is:
eight
'rowers' is the definition.
(eight can mean a crew of eight rowers)
'had dinner we hear' is the wordplay.
'had dinner' becomes 'ate' (I've seen this in another clue).
'we hear' shows a homophone (sound like).
'ate' is a homophone of 'EIGHT'.
(Other definitions for eight that I've seen before include "power of two" , "One less than nineteen across" , "Figure" , "Cube of two" , "Cardinal number" .)