Test on a regular basis -- not really (4)
I believe the answer is:
oral
'test' is the definition.
(I've seen this before)
'on a regular basis not really' is the wordplay.
'on a regular basis' means one should take alternating letters.
'not'+'really'='notreally'
The alternate letters of 'notreally' are 'ORAL'.
(Other definitions for oral that I've seen before include "language exam" , "Vocal test" , "Spoken, of the mouth" , "Ant; tourist (dial.)" , "Spoken test" .)