Incombustibility

Part of speech: noun

Definitions

1. The property of a material that prevents it from igniting or burning when exposed to fire
2. The characteristic of not being flammable or combustible, making something resistant to fire damage
3. A trait describing an object's incapacity to catch fire or sustain combustion under heat or flame

Etymology: Inside this noun is the Latin verb "comburere", meaning "to burn up", built from "com-" (thoroughly) and "urere" ("to burn"). Its past participle "combustus" gave Late Latin "combustibilis", "capable of being burned". Adding the negating prefix "in-" produced "incombustibilis", "not able to be burned up", which is the source of the English adjective "incombustible". English formed the noun by adding the suffix "-ity" to that adjective. The suffix turns a quality into a noun, so the word names the state of being unable to burn rather than any particular fireproof object. "Combustible" shares the same root, so the two words are opposites built on the same verb.