Many a mark made by a prospector (5)
I believe the answer is:
claim
'a prospector' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'many a mark made by' is the wordplay.
'many' becomes 'c' (C is the Roman numeral for l00).
'a mark' becomes 'laim' (I can't explain this - if you can you should believe this answer much more).
'made by' means one lot of letters go next to another (letters written or made by another set of letters).
'c'+'laim'='CLAIM'
Can you help me to learn more?
(Other definitions for claim that I've seen before include "Maintain, assert" , "Allege" , "Assert; demand" , "Take" , "Allegation" .)