It's obvious I must get myself some extra money (8)
I believe the answer is:
overtime
'some extra money' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'it's obvious i must get myself' is the wordplay.
'it's obvious' becomes 'overt' (similar in meaning).
'must get' says to put letters next to each other.
'myself' becomes 'me'.
'overt'+'i'+'me'='OVERTIME'
Can you help me to learn more?
(Other definitions for overtime that I've seen before include "Pay for extra work" , "Hours worked and paid for beyond the usual amount" , "Work in excess of fixed period" , "Work outside normal hours" , "opportunity for supplementing income" .)