Have you ever heard of autological words?

It's a bit of a fancy term, but it just describes any word that follows its own definition. Some examples of autological words include:

  1. Noun (which is itself a noun)
  2. Adjectival
  3. Common (this one's arguable, but humor me)
  4. Meaningful
  5. Writable
  6. Final (which is the last word in this list)

Okay, so you get the idea.

The other day, a friend and I came up with the idea of "cological" words, which are words that can define each other. I think this is a pretty cool concept. Here are some examples:

  1. English and autoglossonym (an autoglossonym is just the name of a language written in that language—think of those "select language" pull-down menus, where each entry obviously should be in the language they describe)
  2. Autological and pentasyllabic (a little confusing at first, but just think about how that works—this one is kind of beautiful)
  3. Shorter and longer (it only works contextually; shorter is longer than longer, and longer is shorter than shorter)
  4. Epistolary and handwritten (which only works if you wrote "epistolary" down somewhere by hand)

This idea can be extended further into "trilogical", which descibes a group of three words that each define both of the other two.

  1. Word, noun, term (boring)
  2. Sesquipedalian, autological, erudite.

Kind of cool, but after a while, finding trilogical groups sort of devolves into a game of just finding three words in a similar category. To solve this problem, I invented borromeological words.

They're called borromeological because the way they define each other is modeled after the Borromean rings, which are a mathematically/topologically significant set of three rings that are interlocked in such a way where removing any one of the three rings frees the other two from the interlocking pattern. Confused? Google an image and you should quickly see how it functions.

Borromeological words are thus words that can define the other two as a group, but not either individually.

I've only found one set of borromeological words so far:

  1. Synonymous, antonymous, opposite.

And therein lies the challenge: Find more valid sets of borromeological words. 

Have at it, and tell me how it goes.