Vain academic welcomed by college board (12)
I believe the answer is:
unprofitable
'vain' is the definition.
(I've seen this before)
'academic welcomed by college board' is the wordplay.
'academic' becomes 'prof'.
'welcomed by' indicates putting letters inside (I've seen this in other clues).
'college' becomes 'uni' (I've seen this in other clues**).
'board' becomes 'table' ('table' can be a synonym of 'board').
'prof' put inside 'uni' is 'unprofi'.
'unprofi'+'table'='UNPROFITABLE'
(Other definitions for unprofitable that I've seen before include "Not beneficial" , "Vain" .)