Tertiary \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. (Zo["o]l.) One of the quill feathers which are borne upon the basal joint of the wing of a bird. See Illust. of Bird.

Source: Webster's Revised Unabridged Dictionary (1913)