tertian

adj

1. (not-comparable)Characterised by paroxysms recurring every other day (that is, every third day by inclusive reckoning).
2. (not-comparable)Pertaining to the mean-tone temperament, in which major thirds are perfectly in tune.

noun

1. A tertian fever.

   “And although we feele it not, it is not to bee doubted, if a continuall ague may in the end suppresse our mind, a tertian will also (according to her measure and proportion) breed some alteration in it.”

   “He died of the slow fever call'd the tertian, / And left his widow to her own aversion.”

2. A cask of a certain size; its volume used as a measure of capacity (one-third of a tun's).
3. A Jesuit going through tertianship.