Academic has nothing in evidence (5)
I believe the answer is:
proof
'evidence' is the definition.
(proof is a kind of evidence)
'academic has nothing' is the wordplay.
'academic' becomes 'prof' (short for professor).
'has' indicates putting letters inside.
'nothing' becomes 'o' (looks like zero - 0).
'prof' placed around 'o' is 'PROOF'.
'in' is the link.
(Other definitions for proof that I've seen before include "Author may have to check this" , "Testimony" , "Body of evidence" , "Demonstration of the truth of something" , "Factual evidence" .)