(relativity) A theory extending special relativity and uniformly accounting for gravity and accelerated frames of reference, postulating that space-time curves in the presence of mass.

(relativity) The principle that only the motion of objects relative to one another can be measured, and that there is no absolute frame of reference.

(meteorology) The ratio of the actual amount of water vapor (absolute humidity) present in the air to the saturation point at the same temperature, usually expressed as a percentage.

(sciences) A measure of the density of a material. The ratio of the density of a substance to the density of water at the same temperature. It is dimensionless and therefore has no units.

(grammar) A subordinate clause that modifies a noun.

(grammar) the superlative (a degree of comparison) when it is used to express the highest degree of something in relation to something else

(physics) The theories of special relativity and general relativity, two theories in physics developed mainly by Albert Einstein at the beginning of the 20th century from which several important results such as the equivalence of matter and energy and the Einstein field equations are derived.

(set theory, of set A "in" set B) The set containing exactly those elements belonging to B but not to A.

A person who is related to another through a common ancestor, and not merely by marriage or adoption.

(mathematics, of two or more numbers) having no factors (except the number 1) in common.