Online dictionaries define the adjectives "autological" and "heterological" as follows:
- A word is autological if and only if it describes itself. For example "short" is autological, since the word "short" is short. "Sophisticated" and "polysyllabic" are also autological.
- A word is heterological if and only if it does not describe itself. Hence "long" is a heterological word, as is "monosyllabic".
Since autological and heterological are opposites, all words are members of either the set of "autological" words, or the set of "heterological" words.
The paradox is this: is the word "heterological" heterological?
There is no consistent answer: if it is, then it isn't; if it isn't, then it is.