Definition of: zero

(zir′ō, zē′rō) noun plural ze·ros or ze·roes
1. The numeral or symbol 0; a cipher. ♦ In nontechnical speech, this symbol is often pronounced (ō).
2. Math. The element of a number system that leaves any element unchanged under addition, in particular, a real number 0 such that a + 0 = 0 + a = a for any real number a.
3. The point on a scale, as of a thermometer, from which measures are counted.
4. Mil. A setting for a gunsight which adjusts both for elevation and wind.
5. The lowest point in any standard of comparison; nullity.
—v.t. ze·roed, ze·ro·ing To adjust (instruments) to an arbitrary zero point for synchronized readings.
—to zero in
1. To bring an aircraft into a desired position, as for bombing or landing.
2. To adjust the sight of (a gun) by calibrated results of firings.
—to zero in on
1. To direct gunfire, bombs, etc., toward (a specific target).
2. To concentrate or focus one's energy, attention, etc., on.
—adjective Without value or appreciable change. [<F zéro <Ital. zero <Arabic sifr. Doublet of CIPHER.]