Definition of "Zero" :

noun: the sight setting that will cause a projectile to hit the center of the target with no wind blowing

noun: the point on a scale from which positive or negative numerical quantities can be measured

noun: a quantity of no importance

noun: a mathematical element that when added to another number yields the same number

verb: adjust (as by firing under test conditions) the zero of (a gun)

"He zeroed in his rifle at 200 yards."

verb: adjust (an instrument or device) to zero value

adjective: indicating the absence of any or all units under consideration

"A zero score."

adjective: indicating an initial point or origin

adjective: having no measurable or otherwise determinable value

"The goal is zero population growth."

adjective: of or relating to the null set (a set with no members)