Millimicron is a unit of length that is equivalent to one-thousandth of a micron or one millionth of a millimeter. Synonyms for millimicron include nanometer, angstrom, and tenth-wave-length. A nanometer is defined as one billionth of a meter and is commonly used in the fields of physics and chemistry to describe the size of molecules and atoms. An angstrom is equivalent to 0.1 nanometers and is commonly used in crystallography and spectroscopy. Tenth-wave-length is a measure of optical wavelength used in the fields of optics and astronomy. While each of these units refer to measures of length on a small scale, they may be used interchangeably in various scientific applications.