mid-15c., "transference of property, grant of land for life or a period of years," via Anglo-French from Old French demis, fem. past participle of desmetre "dismiss, put away" (Modern French démettre), from des- "away" (from Latin dis-) + metre "put," from Latin mittere "let go, send" (see mission).
Originally especially "a conveyance of an estate by will or lease," then "transfer of sovereignty," as by the death or deposing of a king (1540s). The sense was transferred to "death" (as the occasion of such a transfer) by 1754, at first especially the death of a sovereign or other important person, but also as a euphemism for "death."
"the third great geological period," 1841, Cainozoic, from Latinized form of Greek kainos "new, fresh, recent, novel" (see recent) + zōon "animal," but here with a sense of "life" (from PIE root *gwei- "to live"). The era that began with the demise of the dinosaurs and the rise of "recent" species and continues to the present; it also is known as the Tertiary. Compare Paleozoic, Mesozoic.
We observe that Lyell, in his geological works, even the most recent, uses the word Cainozoic instead of Coenozoic or Cenozoic. Why the propounder of the terms Eocene, Miocene, etc., should thus spell the word is incomprehensible. If he is right in it, then to be consistent he ought to say Eocain, Miocain, Pliocain, Post-pliocain; for all have the same root καινός. [American Journal of Sciences and Arts, 1873]