ems

/EH1 M Z/
noun
  1. 1

    The name of the Latin-script letter M.

    โ€œThe ems and ens at the beginnings and ends.โ€

  2. 2

    A unit of measurement equal to the height of the type in use.

Source: https://en.wiktionary.org/wiki/em, https://en.wiktionary.org/wiki/ems