Applauds occasionally, which is a positive (4)
I believe the answer is:
plus
'a positive' is the definition.
(I know that positive can be written as plus)
'applauds occasionally' is the wordplay.
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
The alternate letters of 'applauds' are 'PLUS'.
'which is' acts as a link.
(Other definitions for plus that I've seen before include "Positive sign" , "The opposite of minus" , "And also; a bonus" , "An advantage (colloq.)" , "Distant" .)