Lift's free with key (4)
I believe the answer is:
ride
'lift's' is the definition.
(I've seen this in another clue)
'free with key' is the wordplay.
'free' becomes 'rid' (to be free of something is to be rid of it).
'with' says to put letters next to each other.
'key' becomes 'E' (musical key).
'rid'+'e'='RIDE'
(Other definitions for ride that I've seen before include "Fairground attraction; go on horseback" , "spin > lift > pedal" , "Journey on horse?" , "Travel, by horse say" , "Travel, on horseback, say" .)