tertian

/T EH1 R SH AH0 N/
noun
  1. 1

    A tertian fever.

  2. 2

    The puncheon, an old wine cask, three of which made a tun.

adjective
  1. 1

    (of a fever) Characterised by paroxysms recurring every other day (that is, every third day by inclusive reckoning).

  2. 2

    Pertaining to the mean-tone temperament, in which major thirds are perfectly in tune.

Source: https://en.wiktionary.org/wiki/tertian