Something to remind one in passing (8)
I believe the answer is:
memorial
'passing' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'something to remind one' is the wordplay.
I cannot quite see how this works, but
'one' could be 'me' (a setter might use 'one' to humourously mean 'me') and 'me' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for memorial that I've seen before include "statement of facts" , "Commemorative object" , "Monument to past events" , "may be brass" , "Monument to commemorate" .)