adv. [UN-1 11; cf. prec.] To an unfathomable extent.

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1695.  Blackmore, Pr. Arth., VII. 61. A wide mouth’d Den,… That downward goes unfathomably deep, Beneath the subterranean Vaults.

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1771.  Smollett, Humph. Cl., 3 Sept. A surprising body of pure transparent water, unfathomably deep in many places.

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1820.  Shelley, Witch Atl., xlix. The tremulous stars sparkled unfathomably.

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1833.  Ht. Martineau, Briery Creek, i. 4. His grandfather appeared to him … unfathomably wise.

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