Top-ranking wager covers everything used here (8)
I believe the answer is:
alphabet
'covers everything used here' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'top-ranking wager' is the wordplay.
'top' becomes 'alpha' (I've seen this before).
'ranking wager' becomes 'bet' (synonyms. I am not sure about the 'ranking' bit.).
'alpha'+'bet'='ALPHABET'
Can you help me to learn more?
(Other definitions for alphabet that I've seen before include "Group of characters" , "Whole set of letters" , "Set of characters" , "series of letters" , "needing help on mountain height" .)