quartan, a. [F. quartain, in fièvre 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. [1913 Webster]
quartan, n.
An intermittent fever which returns every fourth day, reckoning inclusively, that is, one in which the interval between paroxysms is two days. [1913 Webster]
A measure, the fourth part of some other measure. [1913 Webster]