the arithmetical symbol 0 or 0̸ denoting the absence of all magnitude or quantity. ADDITIVE IDENTITY. a value of an independent variable that makes a function equal to zero. the absence of a measurable quantity. the point of departure in reckoning. the temperature represented by the zero mark on a thermometer. the setting or adjustment of the sights of a firearm that causes it to shoot to point of aim at a desired range. an insignificant person or thing: NONENTITY. a state of total absence or neutrality. the lowest point: NADIR. something arbitrarily or conveniently designated zero. of, relating to, or being a zero. having no magnitude or quantity: not any. having no phonetic manifestation. having no modified inflectional form. limiting vision to 50 feet (15 meters) or less. limited to 165 feet (50.3 meters) or less. to determine or adjust the zero of. to concentrate firepower on the exact range of —usually used with in. to bring to bear on the exact range of a target —usually used with in. to adjust fire on a specific target —usually used with in. to close in on or focus attention on an objective —usually used with in.