Put right – and that’s definite (5)
I believe the answer is:
fixed
'that's definite' is the definition.
('fixed' can be a synonym of 'definite')
'put right' is the wordplay.
'put' becomes 'fix' (fixing is a kind of putting).
'right' becomes 'ed' (I can't justify this - if you can you should give a lot more credence to this answer).
'fix'+'ed'='FIXED'
'and' is the link.
Can you help me to learn more?
(Other definitions for fixed that I've seen before include "Set" , "Established" , "Securely fastened" , "Arranged" , "Repaired" .)