1660s, from Latin igneus "of fire, fiery," from ignis "fire," from PIE *egni- "fire" (cf. Sanskrit agnih "fire, sacrificial fire," Old Church Slavonic ogni, Lithuanian ugnis "fire").
Relating to rocks or minerals formed by the cooling and hardening of magma or molten lava. Basalt and granite are examples of igneous rocks.
Relating to the processes, such as volcanism, by which such rocks and minerals form.