Fly around Pole? That’s a joke (4)
I believe the answer is:
jest
'that's a joke' is the definition.
(synonyms)
'fly around pole?' is the wordplay.
'fly' becomes 'jet' (jetting is a kind of flying).
'around' is an insertion indicator.
'pole?' becomes 's' (abbreviation for South, as in South Pole).
'jet' enclosing 's' is 'JEST'.
(Other definitions for jest that I've seen before include "attempt at humour" , "Ridicule" , "Banter, joke" , "Act in a joking manner" , "Witty remark" .)