(set theory) The set that contains exactly those elements belonging to the universal set but not to a given set.

(mathematics) The mean of the absolute magnitude of a function that has both positive and negative values.

(astronomy) The intrinsic luminosity that a celestial body would have if viewed from a distance of 10 parsecs or about 32.6 light years.

(grammar) case used to indicate the patient or experiencer of a verb’s action. The absolutive case is used to mark the subject of an intransitive verb, as well as the object of a transitive verb (inasmuch as they are codified in the English nominative-accusative system). Some languages that employ the absolutive case include Abkhaz, Basque, Chechen, Dyirbal, Hindi, Inuktitut, Hiligaynon, and Yup'ik.

(mathematics) For a complex number a+bi, the principal square root of the sum of the squares of its real and imaginary parts, √. Denoted by | |.

(law) the official decree marking the legal end of a marriage, allowing the two people to remarry; it follows the decree nisi after six weeks (in Britain)

(meteorology) In a system of moist air, the ratio of the mass of water vapor present to the volume occupied by the mixture, that is, the density of the water vapor component. Absolute humidity is usually expressed in grams of water vapor per cubic meter or, in engineering practice, in grains per cubic foot. Because this measure of atmospheric humidity is not conservative with respect to adiabatic expansion or compression, it is not commonly used by meteorologists. (Also called vapor concentration and vapor density). See relative humidity.

(physics) The coldest possible temperature, zero on the Kelvin scale, or approximately −273.15 °C, −459.67 °F; total absence of heat; temperature at which motion of all molecules would cease.

In Italian, Spanish, Portuguese, and Catalan: the form of an adjective formed by adding the suffixes -issimo, -ísimo, -íssimo, -érrimo, -imo, or -íssim to the adjective (with any final vowel dropped) to express a superlative that cannot be exceeded, having the sense “as ... as possible”.

(mathematics) The difference (sometimes defined to be the absolute difference) between the measured or inferred value of a quantity and its true value.