unfathomable (adj.)
- abysmal
- abyssal
- all-inclusive
- ambiguous
- bottomless
- boundless
- cavernous
- countless
- endless
- eternal
- gaping
- illimitable
- immeasurable
- immense
- impenetrable
- inarticulate
- incalculable
- incognizable
- incoherent
- incomprehensible
- inexhaustible
- infinite
- innumerable
- inscrutable
- interminable
- limitless
- measureless
- numinous
- perpetual
- rambling
- soundless
- unbounded
- unconnected
- unfathomed
- unintelligible
- universal
- unknowable
- unlimited
- unmeasurable
- unmeasured
- unnumbered
- unplumbed
- unsounded
- untold
- yawning
