D defs.my
Entry 1 sense Webster, 1913

antimatter

/(ăn`tĭ*măt"tẽr)/ · an·ti·mat·ter · IPA /ˈæn.tiˌmæt.ɚ/
01 n. Matter whch is composed of antiparticles such as antiprotons, positrons, and antineutrons.
  1. 1.
    Matter whch is composed of antiparticles such as antiprotons, positrons, and antineutrons.(Physics)