| cryptic(adjective, obscure, difficult, dark, strange) |
| innumerable(adjective, vast, immense, infinite, boundless) |
| occult(adjective, obscure, dark, superior, strange) |
| endless(adjective, complete, deep, abundant, immense) |
| illimitable(adjective, complete, deep, endless, immense) |
| incalculable(adjective, complete, deep, constant, abundant) |
| limitless(adjective, constant, abundant, unrestrained, immense) |
| perplexing(adjective, hard, obscure, difficult, dark) |
| soundless(adjective, depth, bottomless, fathomless) |
| abyssal |
| baffling(adjective, hard, obscure, difficult, solid) |
| esoteric(adjective, hard, obscure, difficult, strange) |
| fathomless(adjective, depth) |
| inexhaustible(adjective, vast, endless, immense, infinite) |
| opaque(adjective, hard) |
| unknowable(adjective, hard, obscure, difficult, solid) |
| unlimited(adjective, constant, abundant, unrestrained, immense) |
| immense(adjective, vast, endless, infinite, boundless) |
| interminable(adjective, constant, abundant, unrestrained, endless) |
| mystifying(adjective, hard, obscure, strange, mysterious) |