Quartan a. : Of or pertaining to the fourth; occurring every fourth day, reckoning inclusively; as, a quartan ague, or fever.

Quartan n. : An intermittent fever which returns every fourth day, reckoning inclusively, that is, one in which the interval between paroxysms is two days.

Quartan n. : A measure, the fourth part of some other measure.

Example:
Which of this diseases of the Renaissance Still exist?

Taxonomy
quartan fever, Merriam-Webster Online Dictionary, Dictionary, webster, Word Games, Webster Online Dictionary with audio pronunciations, Middle English, thesaurus, adjective, glossary, language, ESL, Search, Etymology, Anglo-French, fevre, Latin, febris.

Defination from the web:
quartan from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... Etymology: Middle English quarteyn, from Anglo-French (fevre) quartaine quartan fever, from Latin (febris) quartana, from quartanus of the fourth, ...