# Vulcanism

> English word · Proper noun

## Definitions
1. The belief, held mostly in the 18th century, that rocks were formed in fire. It was a rival theory to Neptunism.

## Etymology
From Vulcan + -ism.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/vulcanism