Round globe - seafarer encircles it (5)
I believe the answer is:
obese
'round' is the definition.
(I've seen this before)
'globe seafarer encircles it' is the wordplay.
'encircles it' says the answer is hidden in the clue.
'OBESE' is hidden within 'globe seafarer'.
(Other definitions for obese that I've seen before include "Morbidly overweight" , "porky?" , "Extremely portly" , "carrying remarkable weight" , "Extremely fat" .)