Rule out time signature in introductory movement (8)
I believe the answer is:
preclude
'rule out' is the definition.
(I know this)
'time signature in introductory movement' is the wordplay.
'time signature' becomes 'c' (I can't explain this - if you can you should believe this answer much more).
'in' indicates putting letters inside.
'introductory movement' becomes 'prelude'.
'c' inserted inside 'prelude' is 'PRECLUDE'.
Can you help me to learn more?
(Other definitions for preclude that I've seen before include "Make impossible" , "Rule out or eliminate" , "bar" , "Prevent (something) from happening" , "'Prevent, forestall (8)'" .)