tertian adjective & noun. ['tǝ:ʃ(ǝ)n] LME.
[Latin (febris) tertiana, from tertius third: see -AN.]
A. adjective.
1. Medicine. Designating a fever recurring every alternate (by inclusive reckoning every third) day; esp. in tertian malaria, arch. tertian ague, the commonest form of malaria due to infection by Plasmodium vivax. LME.

2. Third in order. Now only spec., of or pertaining to the third year of an arts course in some Scottish universities (see sense B.3 below). L16.

3. Music. Relating to the mean-tone temperament in which the major thirds are perfectly in tune. L19.

4. Roman Catholic Church. Tertian Father, a Jesuit undergoing tertianship. L19.
b. noun.
1. Medicine. A tertian fever. LME.
double tertian a fever in which there are two sets of peaks, each of them tertian.

2. A former unit of capacity for liquids, esp. wine or oil, equal to a third of a tun (70 imperial gallons, approx. 318 litres). Also, a large cask of this capacity; a puncheon. obsolete exc. Hist. LME.

3. In some Scottish universities (now only St Andrews), a third-year arts student. E19.

4. Music. A mixture stop in an organ consisting of two ranks of open flue pipes usu. tuned a 17th and 19th above the fundamental. L19.

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