First make out it's not deliberate (7)
I believe the answer is:
mistake
'not deliberate' is the definition.
I can't tell whether this definition defines the answer.
'first make out' is the wordplay.
'first' becomes 'ist' (ist resembles 1st).
'out' means one lot of letters goes inside another.
'ist' going within 'make' is 'MISTAKE'.
'it's' is the link.
Can you help me to learn more?
(Other definitions for mistake that I've seen before include "Oversight" , "Fault" , "Error" , "16 down" , "Slip" .)