An Etymological Dictionary of Astronomy and Astrophysics

A rational number of the form a/b where a is called the numerator and b is called the denominator.

Etymology (EN): From L.L. fractionem (nom. fractio) “a breaking in pieces,” from frangere “to break,” from PIE base *bhreg- “to break” (cf. Goth. brikan, O.E. brecan “to break;” Lith. brasketi
“crash, crack”).

Etymology (PE): Barxé, from barx “lot, portion,” variant bahr, from Mid.Pers. bahr “lot, share, portion,” Av. baxəδra- “portion.”