K-T Definition
adjective
Of or relating to the boundary between the Cretaceous and Tertiary periods, characterized by a mass extinction in which all nonavian dinosaur species perished and by a layer of rock enriched with iridium thought to have originated in one or more asteroid impacts.
American Heritage
Origin of K-T
K short for Cretaceous (used instead of C) (because that letter is often used as an abbreviation of Cambrian) Tertiary
From American Heritage Dictionary of the English Language, 5th Edition
