| impenetrable(adjective, close, hard, tough, solid) |
| impervious(adjective, hard, solid, fast, short) |
| tight(adjective, close, solid, short, substantial) |
| compact(adjective, close, set, hard, tough) |
| hermetic(adjective, tight, proof, impervious, impenetrable) |
| waterproof(adjective, water, tight, proof, impervious) |
| close(adjective, set, hard, tough, solid) |
| dense(adjective, set, hard, tough, firm) |
| impassable(adjective, solid, dense, unaffected, unyielding) |
| sealed(adjective, tight, proof, impervious, impenetrable) |
| thick(adjective, close, set, hard, tough) |
| watertight(adjective, tight, proof, impervious, impenetrable) |
| airtight(adjective, tight, proof, impervious, impenetrable) |
| firm(adjective, close, hard, solid, fast) |
| nonporous(adjective, hard, solid, rigid, resistant) |
| imperviable(adjective, unaffected, unyielding, unbending, resistant) |
| inviolable |
| concrete(hard, solid, rigid, density) |
| hard(adjective, set, tough, firm, solid) |
| proof(adjective, tight, impervious, hermetic) |