Source : Webster's Revised Unabridged Dictionary (1913)

Quartan \Quar"tan\, a. [F. quartain, in fi[`e]vre quartaine, L.
   quartanus, fr. quartus the fourth. See {Quart}.]
   Of or pertaining to the fourth; occurring every fourth day,
   reckoning inclusively; as, a quartan ague, or fever.

Quartan \Quar"tan\, n.
   1. (Med.) An intermittent fever which returns every fourth
      day, reckoning inclusively, that is, one in which the
      interval between paroxysms is two days.

   2. A measure, the fourth part of some other measure.

Source : WordNet®

quartan
     adj : occurring every fourth day (especially the fever and
           weakness of malaria); "quartan malaria"