29 possible answers to
Answers with 3 characters: SET Answers with 4 characters: DEAF FIRM GRIM HARD IRON TAUT Answers with 5 characters: RIGID ADAMT STEEL STERN STONY TOUGH Answers with 6 characters: FLINTY STEELY STRICT Answers with 7 characters: ADAMANT GRANITE STERILE Answers with 8 characters: OBDURATE RESOLUTE HARDLINE STUBBORN Answers with 9 characters: HARDNOSED IRONBOUND STEADFAST Answers with 10 characters: ADAMANTINE INEXORABLE Answers with 11 characters: INDOMITABLE