13 possible answers to
Answers with 4 characters: GRIM Answers with 5 characters: HARSH RIGID STERN Answers with 6 characters: STRICT Answers with 7 characters: ADAMANT AUSTERE EXTREME Answers with 8 characters: HARDCORE HARDLINE Answers with 10 characters: BRASSBOUND RELENTLESS Answers with 13 characters: DYEDINTHEWOOL