igneous

The word 'igneous' is a direct borrowing from the Latin adjective 'igneus', meaning 'fiery' or 'of fire'. Its core morpheme, 'ign-', derives from the Latin noun 'ignis', which traces its origins to the Proto-Indo-European root egni-, also meaning fire. The suffix '-eous' is a common English adaptation of the Latin '-eus', used to form adjectives indicating composition or origin. Thus, the literal meaning 'pertaining to fire' evolved in modern geological terminology to specifically describe rocks formed through the solidification of molten, fiery material from the Earth's interior.

Structure: ign (fire) + eous (adjective suffix) ign (Latin, 'ignis', meaning 'fire'); eous (Latin adjectival suffix '-eus', meaning 'made of' or 'pertaining to').