Male six-footer sounds cheerful! (7)
I believe the answer is:
buoyant
'cheerful' is the definition.
(similar in meaning)
'male six-footer' is the wordplay.
'male' becomes 'buoy' (I can't explain this - if you can you should give a lot more credence to this answer).
'six footer' becomes 'ant' (an ant has six feet).
'buoy'+'ant'='BUOYANT'
'sounds' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for buoyant that I've seen before include "Able to float" , "Bouncy" , "Cheerful, optimistic" , "In good spirits" , "Lively nineteen twenties dance" .)