Ter″ti‐a‐ry, n.; pl.Tertiaries (�). 1. (R. C. Ch.) 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. Addis & Arnold.
2. (Geol.) The Tertiary era, period, or formation.
3. (Zoöl.) One of the quill feathers which are borne upon the basal joint of the wing of a bird. See Illust. of Bird.