n.1 a numerical quantity that is not a whole number (e.g. 1/2, 0.5).
2 a small, esp. very small, part, piece, or amount.
3 a portion of a mixture separated by distillation etc.
4 Polit. any organized dissentient group, esp. a group of communists in a non-communist organization.
5 the division of the Eucharistic bread.
Derivatives:
fractionary adj. fractionize v.tr. (also -ise).
Etymology: ME f. OF f. LL fractio -onis f. L frangere fract- break