Get tense reprimand (4)
I believe the answer is:
twig
'get' is the definition.
(both can mean to understand or realise)
'tense reprimand' is the wordplay.
'tense' becomes 't' (grammatical abbreviation).
'reprimand' becomes 'wig' (wig is a kind of reprimand).
't'+'wig'='TWIG'
(Other definitions for twig that I've seen before include "Cotton on - small branch" , "Get the idea" , "Small tree shoot" , "A small branch - geddit?" , "Only a minor branch" .)