1a numerical quantity that is not a whole number (e.g. 1/ 2, 0.5).
2a small or tiny part, amount, or proportion of something:he hesitated for a fraction of a secondher eyes widened a fraction
a dissenting group within a larger one:the dominant classes or fractions in capitalist societies
3 Chemistry each of the portions into which a mixture may be separated according to a physical property such as boiling point or solubility:the third fraction contain alcohols with boiling points of 120–130°C
4 [mass noun] (usually the Fraction) (in the Christian Church) the breaking of the Eucharistic bread:the Fraction may be accompanied by the Agnus Dei