As a joke, it's less than engaging (3)
I believe the answer is:
gag
'as' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'a joke it's less than engaging' is the wordplay.
'GAG' is hidden in amongst the letters.
But, I am uncertain how this is indicated.
Can you help me to learn more?
(Other definitions for gag that I've seen before include "Retch at the joke?" , "Muzzle or silence" , "that renders one speechless" , "Silence the joke" , "Censor" .)