Show involving Post Office framing worker (5)
I believe the answer is:
panto
'show' is the definition.
(pantomime)
'post office framing worker' is the wordplay.
'post office' becomes 'po' (abbreviation).
'framing' is an insertion indicator (inserted letters are framed by the outside letters).
'worker' becomes 'ant' (worker is a type of ant).
'po' going around 'ant' is 'PANTO'.
'involving' acts as a link.
(Other definitions for panto that I've seen before include "Fun for kids" , "Seasonal show, in short" , "Slapstick theatre for children (abbr)" , "festive entertainment" , "Trad. Christmas fun (abbr.)" .)