Exam not really taken regularly (4)
I believe the answer is:
oral
'exam' is the definition.
(spoken academic test)
'not really taken regularly' is the wordplay.
'taken regularly' indicates alternate letters (letters removed at regular intervals).
'not'+'really'='notreally'
The alternate letters of 'notreally' are 'ORAL'.
(Other definitions for oral that I've seen before include "Via the mouth" , "Viva voce" , "Spoken, of the mouth" , "Spoken exam" , "Verbal" .)