Word for secret or in-joke [closed]

There is a word, somewhere in my dictionary, that means a joke that only a particular group understands i.e., in-joke. I can't remember it and have failed to find it with an online thesaurus, but it is particular to the idea of a joke and not just secret knowledge such as arcane or esoteric.

A bit of humor understood only by a particular group of people is variously called a private joke, inside joke, in-joke, or in joke, roughly in order of usage.

Private joke looks to be the oldest form, with many 19th-Century uses like this one (1890):

Having paid their money, and perhaps foregone the pleasure they could have enjoyed somewhere else, it suddenly comes upon them that they have been taken in, and are sitting in front of the theater only to witness the enjoyment of the actors, who are reveling in some private joke and refuse to let them into the secret....

The three variants of inside joke become common around the 1960s. (In joke is common before that, but earlier uses mean “in jest” rather than “private joke.”)