Notice man's running to grab one purchase (8)
I believe the answer is:
adhesion
'one purchase' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'notice man's running to grab' is the wordplay.
'notice' becomes 'ad' (short for advert).
'man' becomes 'he' (he refers to a man).
'running to' becomes 'sion' (I can't justify this - if you can you should believe this answer much more).
'grab' says to put letters next to each other.
'ad'+'he'+'sion'='ADHESION'
Can you help me to learn more?
(Other definitions for adhesion that I've seen before include "strong attachment" , "Tackiness" , "steady attachment" , "Process of sticking together" , "He's no aid to sticker" .)