Round bees, awfully fat (5)
I believe the answer is:
obese
'fat' is the definition.
(similar in meaning)
'round bees awfully' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'awfully' indicates an anagram.
'bees' is an anagram of 'bese'.
'o'+'bese'='OBESE'
(Other definitions for obese that I've seen before include "likely to tip the balance?" , "Unusually fat" , "Extremely overweight" , "carrying remarkable weight" , "getting well-upholstered" .)