zero

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The numerical symbol 0; a cipher.
• noun The identity element for addition.
• noun A cardinal number indicating the absence of any or all units under consideration.
• noun An ordinal number indicating an initial point or origin.
• noun An argument at which the value of a function vanishes.
• noun The temperature indicated by the numeral 0 on a thermometer.
• noun A sight setting that enables a firearm to shoot on target.
• noun Informal One having no influence or importance; a nonentity.
• noun The lowest point.
• noun Informal Nothing; nil.
• adjective Of, relating to, or being zero.
• adjective Having no measurable or otherwise determinable value.
• adjective Informal Absent, inoperative, or irrelevant in specified circumstances.
• adjective Designating a ceiling not more than 16 meters (52 feet) high.
• adjective Limited in horizontal visibility to no more than 55 meters (180 feet).
• adjective Linguistics Of or relating to a morpheme that is expected by an established, regular paradigm but has no spoken or written form. Moose has a zero plural; that is, its plural is moose.
• transitive verb To adjust (an instrument or a device) to zero value.

from The Century Dictionary.

• noun In function-theory, a value of x which makes the function vanish.
• noun In psychophysics, the temperature at which a thermal stimulus fails to arouse a sensation either of warmth or of cold in the cutaneous organs; the indifference-point of thermal stimulation.
• noun Cipher; the figure 0, which stands for naught in the Arabic notation for numbers.
• noun The defect of all quantity considered as quantity; the origin of measurement stated as at a distance from itself; nothing, quantitatively regarded.
• noun Hence—3. Figuratively, the bottom of the scale; the lowest point or ebb; a state of nullity or inanition.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Arith.) A cipher; nothing; naught.
• noun The point from which the graduation of a scale, as of a thermometer, commences.
• noun Fig.: The lowest point; the point of exhaustion.
• noun See under Absolute.
• noun (Physics) a method of comparing, or measuring, forces, electric currents, etc., by so opposing them that the pointer of an indicating apparatus, or the needle of a galvanometer, remains at, or is brought to, zero, as contrasted with methods in which the deflection is observed directly; -- called also null method.
• noun the point indicating zero, or the commencement of a scale or reckoning.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun cardinal The cardinal number occurring before one and that denotes no quantity or amount at all, represented in Arabic numerals as 0.
• noun The numeric symbol that represents the cardinal number zero.
• noun The digit 0 in the decimal, binary, and all other base numbering systems.
• noun informal, uncountable Nothing, or none.
• noun The value of a magnitude corresponding to the cardinal number zero.
• noun The point on a scale at which numbering or measurement originates.
• noun mathematics A value of the independent variables of a function, for which the function is equal to zero.
• noun mathematics, algebra The additive identity element of a monoid or greater algebraic structure, particularly a group or ring.
• noun slang A person of little or no importance.
• noun military A Mitsubishi A6M Zero, a long range fighter aircraft operated by the Japanese Navy Air Service from 1940 to 1945.
• noun A setting of calibrated instruments such as a firearm.
• noun finance A security which has a zero coupon (paying no periodic interest).
• adjective informal, used with noun none