tertian adj 1: relating to symptoms (especially malarial fever) that appear every other day; "tertian fever" 2: of or relating to a tonal system based on major thirds; "a tertian tonal system"
Tertian \Ter"tian\, a. [L. tertianus, from tertius the third. See {Tierce}.] (Med.) Occurring every third day; as, a tertian fever. [1913 Webster]
Tertian \Ter"tian\, n. [L. tertiana (sc. febris): cf. OF. tertiane.] 1. (Med.) A disease, especially an intermittent fever, which returns every third day, reckoning inclusively, or in which the intermission lasts one day. [1913 Webster] 2. A liquid measure formerly used for wine, equal to seventy imperial, or eighty-four wine, gallons, being one third of a tun. [1913 Webster]