Spooks occasionally risk ringing abrupt PM (7)
I believe the answer is:
rattles
'spooks' is the definition.
Although both the answer and definition are plural nouns, I don't understand how one could define the other.
'occasionally risk ringing abrupt pm' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'ringing' means one lot of letters goes inside another.
'abrupt pm' becomes 'attle' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The alternate letters of 'risk' are 'rs'.
'rs' enclosing 'attle' is 'RATTLES'.
Can you help me to learn more?
(Other definitions for rattles that I've seen before include "Noisy toys for babies" , "Starlet (anag)" .)