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.