How do you spell Tertian

Available Definitions:
1)  a. - Occurring every third day; as, a tertian fever.
2)  n. - A disease, especially an intermittent fever, which returns every third day, reckoning inclusively, or in which the intermission lasts one day.
3)  n. - A liquid measure formerly used for wine, equal to seventy imperial, or eighty-four wine, gallons, being one third of a tun.