zealerhttp://www.oed.com/dictionary/zealer_n%3Ftab%3Dmeaning_and_usezealer, n.
First published 2018

† zealernoun

Obsolete.
  1. ?a1450–1673
    A person who shows zeal (in various senses); esp. (in later use) one who ardently praises, supports, or promotes something.
    Stressed as ˈzealer.
    1. ?a1450
      Zele is double: þat is to sey gode & yuel. Gode zele is somtyme ytake for spousale luffyng... And so God, þat is þe spouse of holy chirche, is a strong zeler... Also þat God is a stronge zeler vengyng into þe 3. & þe 4. generacion.
      in C. von Nolcken, Middle English Translation of Rosarium Theology (1979) 103
    2. 1557
      Persecutours of euyil, zelers of good.
      T. North, translation of A. de Guevara, Diall of Princes iii. xli. f. 219
    3. 1632
      A feruent zealer of monasticall religion.
      J. Porter, Flowers of Lives of Renowned Saincts 193
    4. 1673
      Thou lover and zealer of Iesus.
      R. Strange, translation of J. E. Nieremberg, Of Adoration in Spirit & Truth ii. ix. 192

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

zealer, n. was first published in 2018.