A quarter of a year, a period of three months; specifically a three-month term at school or university.
Origin
Late Middle English; earliest use found in Cursor Mundi: a Northumbrian poem of the 14th century. From Irish ráithe and its equivalent Scottish Gaelic ràithe season, quarter of a year (Early Irish ráithe), perhaps cognate with Welsh rhawd (in gaeafrawd, lit. ‘winter-season’; compare the second element of Early Irish gaimred winter (Irish geimhreadh)), of uncertain origin; perhaps ultimately from an ablaut variant of the Indo-European base of classical Latin rota wheel.