As a joke, it's less than engaging (3)
I believe the answer is:
gag
'as a joke' is the definition.
I can't judge whether this definition defines the answer.
'less than engaging' is the wordplay.
'less' indicates the answer is hidden within the clue (the clue less some of the letters in it).
'GAG' is hidden within 'than engaging'.
'it's' acts as a link.
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" .)