Love of money (7)
'money' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?
'love of' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'o'+'of'='OOF'
Can you help me to learn more?
(Other definitions for avarice that I've seen before include "Greed - caviare (anag)" , "Sway, control" , "Eager desire" , "Insatiable desire for wealth" , "Parsimony" .)