adj
unfathomable
uhn-FA-thuh-muhbl
adj
1
So deep that it cannot be measured.
"The submarine descended into the unfathomable darkness of the trench."
2
Impossible to fully understand or grasp.
"Her grief after the loss was unfathomable to those who hadn't experienced it."
"The scale of the universe is almost unfathomable."
How to Use Unfathomable
Learner’s notesIn plain EnglishToo deep, vast, or complex to measure or understand.
Memory tip
Think of "fathom" as a unit for measuring water depth — "unfathomable" is literally "can't be measured," used mostly for ideas or feelings that are too huge to grasp.
Trace the full origin ↓
Common pairings
unfathomable depths
unfathomable grief
unfathomable mystery
Word Forms
more unfathomable comparative, most unfathomable superlative
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The submarine descended into the _____ darkness of the trench.
Etymology
From un- + fathom (originally, to measure the depth of water) + -able.