| opaque(adjective, set, solid, heavy, deep) |
| petrified(verb, adjective, set, hard, firm) |
| poured(adjective, set, firm, solid, hardened) |
| precast(adjective, set, firm, solid, hardened) |
| quick-frozen |
| refractory(adjective, hard, tough, firm, solid) |
| resistant(adjective, hard, firm, solid, tense) |
| rheumatic(adjective, hard, firm, solid, tense) |
| rigid(adjective, set, hard, tough, firm) |
| ropy(heavy, dense, syrupy, concentrated, viscous) |
| set in stone(expression, adjective, idiom, set, firm) |
| sharp-frozen |
| sloppy(heavy, dense, syrupy, concentrated, viscous) |
| solidify |
| starched(verb, adjective, hard, firm, solid) |
| starchy(adjective, hard, firm, solid, tense) |
| stark(adjective, hard, firm, solid, tense) |
| steeled(verb, adjective, set, firm, solid) |
| steely(adjective, hard, firm, solid, tense) |
| stiff as a board(expression, adjective, idiom, firm, solid) |