Eddy outgrew fifth bikini for full bottoms (5)
I believe the answer is:
whirl
'eddy' is the definition.
(synonyms)
'outgrew fifth bikini for full bottoms' is the wordplay.
'bottoms' suggests the final letters (I've seen 'bottoms of' mean this).
The final letters of 'outgrew fifth bikini for full' are 'WHIRL'.
(Other definitions for whirl that I've seen before include "Circular movement - brief try" , "Quick dance" , "quick turn" , "Eddy" , "Revolve" .)