Word Study
quintan
CIDE DICTIONARY
quintan, 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. [1913 Webster]
OXFORD DICTIONARY
quintan, adj. (of a fever etc.) recurring every fifth day.
Etymology
L quintana f. quintus fifth
For further exploring for "quintan" in Webster Dictionary Online