Returning show restricted by extremely corny humour (6)
I believe the answer is:
comedy
'humour' is the definition.
(comedy is a kind of humour)
'returning show restricted by extremely corny' is the wordplay.
'returning' shows that the letters should be reversed in order.
'show' becomes 'demo' (I've seen this before).
'restricted by' indicates putting letters inside (inserted letters are restricted or trapped).
'extremely' suggests removing the centre (only the extremes of the word are used).
'corny' with its middle removed is 'cy'.
'demo' back-to-front is 'omed'.
'omed' placed inside 'cy' is 'COMEDY'.
(Other definitions for comedy that I've seen before include "farce, perhaps" , "Humour" , "provides amusement" , "Humorous entertainment" , "fun" .)