A real number that cannot be expressed as a rational number.

synonym: irrational.

Roget 84: number, symbol, numeral, figure, cipher, digit, integer; counter; round number; formula; function; series.    sum, difference, complement, subtrahend; product; multiplicand, multiplier, multiplicator^†; coefficient, multiple; dividend, divisor, factor, quotient, submultiple [Math.]; fraction, rational number; surd, irrational number; transcendental number; mixed number, complex number, complex conjugate; numerator, denominator; decimal, circulating decimal, repetend; common measure, aliquot part; prime number, prime, relative prime, prime factor, prime pair; reciprocal; totient^†.    binary number, octal number, hexadecimal number [Comp.].    permutation, combination, variation; election.    ratio, proportion, comparison etc. 464; progression; arithmetical progression, geometrical progression, harmonical progression^†; percentage, permilage.    figurate numbers^†, pyramidal numbers, polygonal numbers.    power, root, exponent, index, logarithm, antilogarithm; modulus, base.    differential, integral, fluxion^†, fluent.    ... show more

Dutch: irrationaal getal
Polish: niepoliczalność, niemierzalność, niewymierność