quartile (n.) Look up quartile at Dictionary.com
c. 1500, originally in astronomy; see quartile (adj.). In statistics, from 1879.
quartile (adj.) Look up quartile at Dictionary.com
mid-15c., "90 degrees apart" (of astronomical measurements), from Middle French quartil, from Medieval Latin quartilus "of a quartile," from Latin quartus "the fourth, fourth part," which is related to quattuor "four," from PIE root *kwetwer- "four."