Definitions of metric:

• noun:   a system of related measures that facilitates the quantification of some particular characteristic
• noun:   a decimal unit of measurement of the metric system (based on meters and kilograms and seconds)

  Example: "Convert all the measurements to metric units"

• noun:   a function of a topological space that gives, for any two points in the space, a value equal to the distance between them
• adjective:   based on the meter as a standard of measurement

  Example: "The metric system"

• adjective:   the rhythmic arrangement of syllables