An Etymological Dictionary of Astronomy and Astrophysics

1a) (n.) An adherent of any of those Christian bodies that separated from the Church of Rome during the Reformation, or of any group descended from them.

1b) (originally) Any of the German princes who protested against the decision of the Diet of Speyer in 1529, which had denounced the Reformation.

1c) (lowercase) One who makes or enters a protests.

2a) (adj.) Belonging or pertaining to Protestants or their religion.

2b) (lowercase) protesting (Dictionary.com).

Etymology (EN): From Ger. or Fr. protestant, from L. protestantem (nominative protestans), p.p. of protestari, → protest.

Etymology (PE): Pâxosân agent noun or adj. from pâxosidan, → protest.