Additional pay for a sincere sort (8)
I believe the answer is:
increase
'additional pay' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'a sincere sort' is the wordplay.
'sort' indicates an anagram.
'a'+'sincere'='asincere'
'asincere' with letters rearranged gives 'INCREASE'.
'for' is the link.
Can you help me to learn more?
(Other definitions for increase that I've seen before include "step up" , "Grow bigger" , "boost" , "extra money at work" , "Become bigger or greater in amount" .)