unfathomable means impossible to fathom.; Especially of depth: physically incapable of being measured; immeasurable. Lexicurio rates it Rare gem — a strength score of 75 out of 100.
Why this word is great
UNFATHOMABLE — [Adjective] Impossible to measure the depth of, or to fully understand or comprehend. From the prefix un- ("not") + fathom (from Old English fæðm, "the span of two outstretched arms," later a nautical unit of depth, and figuratively "to understand") + the suffix -able ("capable of"). Unlike "inscrutable," which suggests an impenetrable surface actively resisting scrutiny, or "immeasurable," which denotes a sheer lack of quantifiable extent, "unfathomable" speaks to a passive, inherent depth that defeats the mind's plumb-line. It is the absolute darkness of a deep-sea trench absorbing the last glimmer of light, the silent calculus behind a stranger's act of sudden mercy, or the vertigo of staring into a night sky whose stars are already dead. Some depths are not for plumbing, only for beholding from the shuddering deck of our understanding.
adj
- Impossible to fathom.; Especially of depth: physically incapable of being measured; immeasurable.“[W]e are not to make our eſtimate of the quantity of VVaters meerly by the Superficies of the Sea, but by its vaſt depth, vvhich in ſome places is unfathomable, and by thoſe vaſt ſubterraneous Receptacles of VVater vvhich pour themſelves out in ſeveral great Ebullitions and Marine Springs: […]”
- Impossible to fathom.; Impossible to grasp the extent of, or to fully know or understand.“The sheer number of warriors the enemy attacked with was unfathomable.”