Number set out principles (6)
I believe the answer is:
tenets
'principles' is the definition.
(a tenet is a principle or belief)
'number set out' is the wordplay.
'number' becomes 'ten' (ten is a kind of number).
'out' is an anagram indicator (out can mean wrong or inaccurate).
'set' with letters rearranged gives 'ets'.
'ten'+'ets'='TENETS'
(Other definitions for tenets that I've seen before include "Doctrines held to be true" , "Beliefs or creeds" , "Canons and creeds" , "Doctrines or dogmas" , "Principles of belief" .)