micron vs. nanometer

noun

plural

microns, micra 
  1. Also called micrometerthe millionth part of a meter. μ, mu

  2. Physical Chemistry.,  a colloidal particle whose diameter is between 0.2 and 10 microns.

  3. Physics.,  a very small unit of pressure, equal to that exerted by a column of mercury 1μ high.

noun

  1. one billionth of a meter. nm