Definition of millimeter noun from the Oxford Advanced American Dictionary

      

    millimeter

     noun
    (millimetre)noun
    NAmE//ˈmɪləˌmit̮ər//
     
    (abbreviation mm)
     
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  1. 1  a unit for measuring length; a 1,000th of a meter
  2. 2(informal) The bullet missed his head by a millimeter.