n. pl. tau·tol·o·gies
a. Needless repetition of the same sense in different words; redundancy.
b. An instance of such repetition.
2. Logic A statement composed of simpler statements in such a way that it is logically true whether the simpler statements are factually true or false; for example, the statement Either it will rain tomorrow or it will not rain tomorrow.
[Late Latin tautologia, from Greek tautologiā, from tautologos, redundant : tauto-, tauto- + logos, saying; see -LOGY.]
tau′to·logi·cal (tôt′l-ŏjĭ-kəl), tau′to·logic (-ĭk), tau·tolo·gous (-tŏlə-gəs) adj.
tau′to·logi·cal·ly, tau·tolo·gous·ly adv.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.