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Definition of tertiary

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ter·ti·ar·y  audio  (tûrsh-r) KEY 

  1. Third in place, order, degree, or rank.
  2. Of, relating to, or designating the short flight feathers nearest the body on the rear edge of a bird's wing.
  3. Chemistry
    1. Of or relating to salts of acids containing three replaceable hydrogen atoms.
    2. Of or relating to organic compounds in which a group, such as an alcohol or amine, is bound to three nonelementary radicals.
  4. Tertiary Of or belonging to the geologic time, system of rocks, or sedimentary deposits of the first period of the Cenozoic Era, characterized by the appearance of modern flora and of apes and other large mammals. See Table at geologic time.
pl. ter·ti·ar·ies
  1. A tertiary feather.
  2. Tertiary The Tertiary Period or its system of deposits.
  3. Roman Catholic Church A member of a religious Third Order.

Latin tertirius, from tertius, third; see trei- in Indo-European roots

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