Definition

1. Noun:
   • A unit of length in the metric system: A "millimicron" is a specific measurement of distance. It is equal to one billionth (1/1,000,000,000) of a meter.

Usage Notes

• The term "millimicron" is an older, non-SI unit of length. In modern scientific contexts, the term nanometer (nm) is the standard and preferred term for this measurement. One millimicron is exactly equal to one nanometer.
• It was historically used in fields like physics and chemistry to measure wavelengths of light or atomic-scale distances.

Examples

• Noun:
  • The wavelength of visible light is measured in hundreds of millimicrons.
  • This filter only allows particles smaller than ten millimicrons to pass.

Advanced Usage

• The term is largely obsolete but may appear in older technical literature. When encountered, it can be directly converted to nanometers (nm).
  • The cell membrane has a thickness of approximately 7.5 millimicrons (7.5 nm).

Variants and Related Words

• Nanometer (nm) (n): The modern SI unit for one billionth of a meter. This is the standard term that has replaced "millimicron."
• Micron (μm) (n): A unit of length equal to one millionth of a meter. Note: A micron.
• Angstrom (Å) (n): A unit of length equal to 0.1 nanometers or 0.1 millimicrons, commonly used in crystallography and atomic physics.

Synonyms

• Nanometer: The direct and modern equivalent term.

Notes on Meaning

• The "milli-" prefix in this context can be confusing. It does not mean one-thousandth of a micron (which would be a nanometer). Historically, "millimicron" was formed to mean a "thousandth of a micron," but since a micron is a millionth of a meter, a thousandth of a micron is indeed a billionth of a meter. The term is essentially synonymous with "nanometer."

Noun

1. a metric unit of length equal to one billionth of a meter