Some cavort, executing whirling motion (6)
I believe the answer is:
vortex
'whirling motion' is the definition.
(I've seen this before)
'some cavort executing' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'VORTEX' is hidden within 'cavort executing'.
(Other definitions for vortex that I've seen before include "Whirlpool - whirlwind" , "Revolutionary movement" , "Engulfing spiral" , "Powerful circular current of water" , "Whirling fluid" .)