The term 'set in stone' is an idiom that means something is permanent and unchangeable. The crossword solutions for this term are FINAL (5 letters), INEXORABLE (10 letters), and ETCH (4 letters). FINAL means something that is complete and cannot be changed, while INEXORABLE means something that is unyielding and unchangeable. ETCH means to carve or engrave a design into a hard surface, which is a metaphor for something that is permanent and unchangeable.