A part of one sort of pedestrian crossing (8,5)
I believe the answer is:
stepping stone
'sort of pedestrian crossing' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'a part of one' is the wordplay.
I cannot really understand how this works, but
'a' could be 'one' and 'one' is located in the answer.
'part' could be 'pin' (pin is a kind of part) and 'pin' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for stepping stone that I've seen before include "Aid to gradual progress" , "Means to gradual progress" , "means of advancement" , "means to get better" , "Footrest in river" .)