millimicron

[mil-uh-mahy-kron] /ˈmɪl əˌmaɪ krɒn/
noun, plural millimicrons, millimicra
[mil-uh-mahy-kruh] /ˈmɪl əˌmaɪ krə/ (Show IPA)
1.
a unit of length equal to one thousandth of a micron; one-billionth of a meter. Symbol: mμ.
Compare nanometer.
Origin
1900-05; milli- + micron
British Dictionary definitions for millimicron

millimicron

/ˈmɪlɪˌmaɪkrɒn/
noun
1.
an obsolete name for a nanometre; one millionth of a millimetre
millimicron in Medicine

millimicron mil·li·mi·cron (mĭl'ə-mī'krŏn)
n.

Abbr. mμ A unit of length that is equal to one thousandth (10-3) of a micrometer or one billionth (10-9) of a meter; nanometer.