A kind of proof calculus in which logical reasoning is expressed by inference rules closely related to the "natural" way of reasoning, in contrast to axiomatic systems.

(evolutionary theory) A process by which heritable traits conferring survival and reproductive advantage to individuals, or related individuals, tend to be passed on to succeeding generations and become more frequent in a population, whereas other less favourable traits tend to become eliminated; the differential survival and reproduction of phenotypes.

A mixture of gaseous hydrocarbons associated with petroleum deposits; mostly methane with smaller amounts of ethane, propane and butane; principally used as a fuel.

(mathematics) The set of positive integers, {1, 2, 3, ...}. / (mathematics, computer science) The set of non-negative integers, {0, 1, 2, 3, ...}.

(mathematics) a positive integer {1, 2, 3, ...} / (mathematics) a non-negative integer {0, 1, 2, ...}

(music) A musical grammar which arises spontaneously in a musical culture (as opposed to an artificial grammar).

A male biological child, whether legitimate or illegitimate, as opposed to one adopted. / An illegitimate son.

Any source of wealth that occurs naturally, especially minerals, fossil fuels, timber, etc.

Any science involved in studying phenomena or laws of the physical world: physics, chemistry, biology, astronomy, and so on.

Any natural phenomenon that causes great damage and loss of life. / The emergency situation that is the consequence of such an event.