The term 'nonflammable' is used to describe materials that are resistant to burning or catching fire. This term can be represented by two crossword solutions: 'FIREPROOF' (9 letters) and 'UNBURNABLE' (10 letters). FIREPROOF materials are those that are not easily ignited and do not burn quickly, while UNBURNABLE materials are those that cannot be burned at all. Both terms refer to materials that are resistant to fire and will not catch fire easily.