'Duck Soup', comedy often tickling everyone's ribs initially (6)
I believe the answer is:
scoter
'duck' is the definition.
(scoter is a kind of duck)
'soup comedy often tickling everyone's ribs initially' is the wordplay.
'initially' suggests taking the first letters.
The first letters of 'soup comedy often tickling everyones ribs' is 'SCOTER'.
(Other definitions for scoter that I've seen before include "Northern diving duck" , "Sea diver" , "Sea duck" , "Diving duck - corset (anag)" , "Species of diving duck" .)