Definition of "quaternary" []

• Consisting of four; in fours. (adjective)
• Of or belonging to the geologic time, system of rocks, or sedimentary deposits of the second period of the Cenozoic Era, from the end of the Tertiary Period through the present, characterized by the appearance and development of humans and including the Pleistocene and Holocene epochs. See Table at geologic time. (adjective)
• Chemistry Relating to an atom bonded to four carbon atoms: a quarternary nitrogen atom. (adjective)
• The number four. (noun)
• The member of a group that is fourth in order. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "But basically we are in what is called the quaternary period and for the past 200,000 years we have been going in and out of ice ages."
• "Other injuries caused by an explosion, such as burns, are called quaternary injuries."
• "TIERNO: That you should leave that material wet for ten minutes because these wipes have what's called quaternary ammonium compounds in them, and that takes at least ten minutes to really effectively work."