| enclosed(adjective, tight, proof, impervious, hermetic) |
| esoteric(adjective, obscure, dark, secret, unknown) |
| gas-tight(adjective, tight, proof, impervious, hermetic) |
| gas proof(adjective, tight, proof, impervious, hermetic) |
| gastight(adjective, tight, proof, impervious, hermetic) |
| hermetically-impervious(adjective, tight, proof, impervious, hermetic) |
| hermetically-sealed(adjective, tight, proof, impervious, hermetic) |
| imperceivable(adjective, obscure, dark, unknown, hidden) |
| impermeable(adjective, tight, proof, impervious, hermetic) |
| impervious |
| in the dark(expression, idiom, obscure, dark, unknown) |
| indiscernible(obscure, dark, secret, unknown, hidden) |
| invisible(obscure, dark, secret, unknown, hidden) |
| latent(obscure, dark, secret, unknown, hidden) |
| leaktight(adjective, tight, proof, impervious, hermetic) |
| liquid-tight(adjective, tight, proof, impervious, hermetic) |
| magic |
| mysterious(obscure, dark, secret, unknown, hidden) |
| mystic(obscure, dark, secret, unknown, hidden) |
| mystical(adjective, obscure, dark, secret, unknown) |