zone-levellerhttp://www.oed.com/dictionary/zone-leveller_n%3Ftab%3Dmeaning_and_usezone leveller, n.
First published 1986; not fully revised

zone levellernoun

  1. 1956–
    An apparatus used for zone levelling.
    1. 1956
      A zone leveler has been developed to provide growth conditions suitable for the production of quality germanium single crystals.
      Bell System Technical Journal vol. 35 660

Originally published as part of the entry for zone, n.

zone, n. was first published in 1921; not fully revised.