The tanner's son, we hear (3)
I believe the answer is:
sun
'the tanner's' is the definition.
(the sun gives people sun tans)
'son we hear' is the wordplay.
'we hear' indicates a 'sounds like' (homophone) clue.
'son' is a homophone of 'SUN'.
(Other definitions for sun that I've seen before include "Hub of our planetary system" , "Centre of a solar system" , "Source of light and heat" , "British publication" , "Major star" .)