(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.

(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.

(retronym, linguistics) Any human language that has evolved naturally in a community, usually in contrast to computer programming languages, to controlled natural languages, and to constructed languages such as Esperanto (although constructed languages are subject to change by natural forces among fluent speakers).

(mathematics) The logarithm in base e: either the function that given x returns y such that eʸ = x, or the value of y given by the function.

(biochemistry) Any compound produced naturally by a living organism; especially those compounds that are useful commercially

(immunology) A natural killer cell

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.