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milliarcsecond
milliarcsecond n.
Brit. 
/ˌmɪlɪˈɑːkˌsɛk(ə)nd/
, /ˌmɪlɪˈɑːkˌsɛk(ə)nd/U.S. /ˌmɪliˌɑrkˈsɛkən(d)/
one thousandth of an arc second./ˌmɪliˌɑrkˈsɛkən(d)/ΚΠ
1979 Nature 9 Aug. 477/2 These errors amount at most to a few milliarcseconds per year in proper motion.
1992 S. P. Maran Astron. & Astrophysics Encycl. 38/1 Very wide field instruments such as Schmidt telescopes can be used for astrometry but accuracies are rarely better than 100 milliarcseconds.
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