Make money and set out to be serious (7)
I believe the answer is:
earnest
'serious' is the definition.
(similar in meaning)
'make money and set out' is the wordplay.
'make money' becomes 'earn' (to earn is to make money).
'and' is a charade indicator (letters next to each other).
'out' is an anagram indicator (out can mean wrong or inaccurate).
'set' with letters rearranged gives 'est'.
'earn'+'est'='EARNEST'
'to be' is the link.
(Other definitions for earnest that I've seen before include "Serious, solemn" , "serious attention" , "Sincere -- humourless" , "Fervent - down payment" , "Determined - heartfelt" .)