The study of all living things, especially their origins, evolution and interrelationships. / The study of all natural phenomena: botany, zoology, mineralogy, etc.

(mathematics) An ordinary trigonometric function

(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).

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

(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.

(immunology) A natural killer cell

(mathematics) natural logarithm

plural of natural harmonic

(music) a sound produced by lightly touching the string as opposed to pressing it against the fingerboard, usually with the actual pitch notated

(Britain, business) Decrease of workforce caused by non-replacement of retiring or voluntarily resigning employees and not by deliberate layoffs.