1. Being of the third formation, order, or rank; third; as, a tertiary use of a word.

2. <chemistry> Possessing some quality in the third degree; having been subjected to the substitution of three atoms or radicals; as, a tertiary alcohol, amine, or salt. Cf. Primary, and Secondary.

3. <geology> Later than, or subsequent to, the Secondary.

4. <zoology> Growing on the innermost joint of a bird's wing; tertial; said of quills. Tertiary age.

<medicine> The third and last stage of syphilis, in which it invades the bones and internal organs.

Origin: L. Tertiarius containing a third part, fr. Tertius third: cf. F. Tertiaire. See Tierce.

1. A member of the Third Order in any monastic system; as, the Franciscan tertiaries; the Dominican tertiaries; the Carmelite tertiaries. See Third Order, under Third.

2. <geology> The Tertiary era, period, or formation.

3. <zoology> One of the quill feathers which are borne upon the basal joint of the wing of a bird.

(01 Mar 1998)