QUARTAN
Source: 566, 567
quartan. Quartan, n. a fourth day argue; a. every fourth day
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Quar″tan (?), 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.