Mark puts the kettle on, we hear (6)
I believe the answer is:
bruise
'mark' is the definition.
(mark left by an injury)
'puts the kettle on we hear' is the wordplay.
'puts the kettle on' becomes 'brews' (to brew is to make a cup of tea).
'we hear' shows a homophone (sound like).
'brews' sounds like 'BRUISE'.
(Other definitions for bruise that I've seen before include "Injury mark; sounds like ferments" , "Discoloured injury" , "Discolouration left by a blow" , "Sign of injury" , "Skin injury" .)