Source : Webster's Revised Unabridged Dictionary (1913)

Quintan \Quin"tan\, a. [L. quintanus, fr. quintus fifth, quinque
   five. See {Five}.]
   Occurring as the fifth, after four others also, occurring
   every fifth day, reckoning inclusively; as, a quintan fever.
   -- n. (Med.) An intermittent fever which returns every fifth
   day, reckoning inclusively, or in which the intermission
   lasts three days.