/ Dictionary / Index M megathere: Meaning and Definition of Find definitions for: meg•a•there Pronunciation: (meg'u-thēr"), [key] — n. any of the huge, slothlike animals of the extinct genus Megatherium, or closely related genera, that lived from the Oligocene to the Pleistocene epochs. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: megathere (Thesaurus) megastructure megatherm Related Content Daily Word Quiz: perspicacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language