Speed to turn in spin (6)
I believe the answer is:
rotate
'spin' is the definition.
(I know that spin is a more specific form of rotate)
'speed to turn in' is the wordplay.
'speed' becomes 'rate' (the speed at which something happens).
'turn' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'to' anagrammed gives 'ot'.
'rate' enclosing 'ot' is 'ROTATE'.
(Other definitions for rotate that I've seen before include "Spin as on axle" , "Turn round" , "Spin round" , "Make to spin around" , "Turn around as on axle or spit" .)