tertian

Etymology

From Middle English tertiān, terciān, terciāne (adjective and noun), originally often as part of the collocation fever cum terciane, after Latin febris cum tertiānā. Compare the "third" essence of tertiary.

adj

1. (medicine, of a fever) Characterised by paroxysms recurring every other day (that is, every third day by inclusive reckoning).
2. (music) Pertaining to the mean-tone temperament, in which major thirds are perfectly in tune.

noun

1. A tertian fever.
   He died of the slow fever call'd the tertian, / And left his widow to her own aversion. 1819, Lord Byron, Don Juan, Canto 1
2. The puncheon, an old wine cask, whose volume was one-third of a tun's.