Dissenter and non-conformist are terms specifically applied to English subjects who hold themselves aloof from the Church of England; the former term is extended to non-adherents of the established church in some other countries, as Russia.

J. C. Fernald, English Synonyms and Antonyms (1914)

Example sentences

protester The police officer beat the protester with her nightstick.
dissident The political dissident has spent nearly a decade under house arrest.
heretic Tom was burnt at the stake as a heretic.
objector I know that Tom was a conscientious objector.

Popularity over time

Word	1850 → 2019	Trend
dissenter		steady
protester		steady
dissident		steady
heretic		rising
objector		falling

Use in printed books, per decade from 1850 to 2019.

By length

7 letters: heretic³, sectary, refuser
8 letters: objector³, recusant
9 letters: dissident³, protester³, refusenik³
10 letters: contestant³, separatist⁴, schismatic

The small number after each word is its number of syllables (heretic³ = 3 syllables).