plural of REL

Initialism of Russo-European Laika.

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

(grammar) A pronoun that introduces a relative clause and refers to an antecedent. Some words that can be used as interrogative pronouns can alternatively be used as relative pronouns: what, which, who, and whom. The other relative pronouns are whoever, whomever, whatever, and that.

(grammar) A relative pronoun used in an adjectival clause.

(relativity) A theory that (neglecting the effects of gravity) reconciles the principle of relativity with the observation that the speed of light is constant in all frames of reference.

(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.