| a. | 1. | (Med.) Occurring every third day; |
| n. | 1. | (Med.) A disease, especially an intermittent fever, which returns every third day, reckoning inclusively, or in which the intermission lasts one day. |
| 2. | A liquid measure formerly used for wine, equal to seventy imperial, or eighty-four wine, gallons, being one third of a tun. |
| Adj. | 1. | tertian - relating to symptoms (especially malarial fever) that appear every other day; "tertian fever" |
| 2. | tertian - of or relating to a tonal system based on major thirds; "a tertian tonal system" |