(firearms) The adjustment of a sight, exactly parallel to the axis of the bore of the gun to which it is attached.

(geometry) Having zero dimensions; having no extent in any direction.

The start of the first hour of the day on the 24-hour clock, i.e. 0:00, military time.

(military) The location of the center of a burst of a nuclear weapon at the instant of detonation. The zero point may be in the air, or on or beneath the surface of land or water, depending upon the type of burst, and it is thus to be distinguished from ground zero.

(physics) associated with zero on any scale, but particularly with a temperature of absolute zero

The state of apparent weightlessness which occurs in a very low gravity field, or in free fall.

(logic) Describing situations in which the veracity of a statement may be shown to be true without revealing any other information.

(US) The smallest size of women's clothing / (informal) A woman with a very low body mass index, especially such a fashion model

A tensor with all entries equal to zero; where any pattern of covariant and contravariant indices have all components equal to 0. / A generalization of the zero vector to tensor space.

atmospheric air specially cleaned so that it contains less than 0.1 ppm of hydrocarbon impurities; it then is usable in laboratory procedures such as versions of gas chromatography in which sufficiently pure air may serve as a carrier gas.