element

1. Smallest entity that is capable of possessing chemical characteristics and that cannot be changed into smaller neutral units by chemical reaction.

Elements in their pure form may exist in atomic forms, for example, He, Ne, or may be associated into molecular units such as H₂, O₂, graphite, or diamond.

1. Any one of the properties or conditions of the atmosphere that together specify the physical state of weather or climate at a given place for any particular moment or period of time; the climatic elements, meteorological elements.
   
2. The smallest definable object of interest in a scene.
   It is a single item in a collection, population, or sample.

1. The product of a distance and another parameter.

Any function of time f(t) is periodic with period t if f(t) = f(t + τ) for all times t, where τ is the smallest number for which this equality holds.