An autological word (also called homological word) is a word that expresses a property that it also possesses (e.g., "word" is a word, "noun" is a noun, "English" is an English word, "pentasyllabic" has five syllables, and "writable" is writable). The opposite is a heterological word, one that does not apply to itself (e.g. the word "long" is not long, "monosyllabic" has more than one syllable, "dactyl" is not a dactyl, and "misspelled" is not misspelled.)

Unlike more general concepts of autology and self-reference, this particular distinction and opposition of "autological" and "heterological words" is uncommon in linguistics for describing linguistic phenomena or classes of words, but is current in logic and philosophy where it was introduced by Kurt Grelling and Leonard Nelson for describing a semantic paradox, later known as Grelling's paradox or the Grelling–Nelson paradox.