Occurring every third day; as, a tertian fever.

A disease, especially an intermittent fever, which returns every third day, reckoning inclusively, or in which the intermission lasts one day.

A liquid measure formerly used for wine, equal to seventy imperial, or eighty-four wine, gallons, being one third of a tun.

a branch of music theory that describes chords as pitches stacked on top of each other separated by the interval of a third. This theory is the basis for most tonal music.

relating to symptoms (especially malarial fever) that appear every other day; "tertian fever"

of or relating to a tonal system based on major thirds; "a tertian tonal system"

a harmony based on chords that are composed of stacked thirds. Derived from the overtone series, tertian harmony forms the basis for what we commonly call tonal music.

In music or music theory, tertian is the quality of a chord constructed from thirds, and other things constructed from thirds such as counterpoint.