The ability to move quickly and easily (7)
I believe the answer is:
agility
'the ability to move quickly and easily' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for agility that I've seen before include "The ability to move quickly and easily" , "Physical ability to move nimbly and quickly" , "Physical nimbleness, easy movement" , "dexterity" , "Litheness" .)