[quar.tan] adj [ME quarteyne, fr. MF (fievre) quartaine quartan fever, fr. L (febris) quartana, fr. quartanus of the fourth, fr. quartus] (14c): occurring every fourth day reckoning inclusively; specif: recurring at approximately 72-hour intervals
[2]quartan n (14c): an intermittent fever that recurs at approximately 72-hour intervals; esp: a quartan malaria