unfathomable

comparative more unfathomable · superlative most unfathomable

1. Impossible to fathom.
   1. Especially of depth: physically incapable of being measured; immeasurable.

      [Y]e may well look up surprised / To those unfathomable heavens that feed / Your purple hills!

      1851, Elizabeth Barrett Browning, Casa Guidi Windows. A Poem, London: Chapman & Hall, […], →OCLC, part I, stanza XIX, page 52

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      [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: […]

      a. 1677 (date written), Matthew Hale, “A Fifth Consideration Concerning the Decays especially of the Humane Nature, and whether there be any such Decays; and what may be Collected Concerning the Origination of Man upon that Supposition”, in The Primitive Origination of Mankind, Considered and Examined According to the Light of Nature, London: […] William Godbid, for William Shrowsbery, […], published 1677, →OCLC, section II, page 187

      But if we yet rise higher, and consider the fixed stars as so many vast oceans of flame, that are each of them attended with a different set of planets, and still discover new firmaments and new lights, that are sunk farther in those unfathomable depths of ether, so as not to be seen by the strongest of our telescopes, we are lost in such a labyrinth of suns and worlds, and confounded with the immensity and magnificence of nature.

      1712 July 12 (Gregorian calendar), [Joseph Addison], “TUESDAY, July 2, 1712. Paper X. On the Pleasures of the Imagination.”, in The Spectator, number 420; republished in Alexander Chalmers, editor, The Spectator; a New Edition, […], volume V, New York, N.Y.: D[aniel] Appleton & Company, 1853, →OCLC, page 79

      Now, where the fiercest war among the waves / Is calm, on the unfathomable stream / The boat moved slowly.

      1815 September 10 – December 14, Percy Bysshe Shelley, “Alastor; or, The Spirit of Solitude”, in Alastor; or, The Spirit of Solitude: And Other Poems, London: […] Baldwin, Cradock, and Joy, […]; and Carpenter and Son, […] [b]y S[amuel] Hamilton, […], published 1816, →OCLC, page 26

      Not till her nineteenth year had she seen the long, dazzling boulevards stretching into unfathomable distance before her eyes; […]

      [1879], [Mary Elizabeth Braddon], “La Chicot”, in The Cloven Foot […], volume I, London: John and Robert Maxwell […], →OCLC, page 71

      Synonyms: abyssal, incalculable, inestimable, soundless, unplumbable, unsoundable · Antonyms: calculable, estimable, fathomable, measurable, plumbable, soundable

   2. figurativelyImpossible to grasp the extent of, or to fully know or understand.

      The sheer number of warriors the enemy attacked with was unfathomable.

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      There are indeed unfadomable depths in that Ocean [i.e., the holy scriptures], vvherin vve ſhall vainly hope to pitch our anchor; but all neceſſary truthes need not much line: […]

      1640, Jos: Exon. [i.e., Joseph Hall], “§. VII. The Fourth Rule of Moderation; to Rest in Those Fundamentall Truthes which are Revealed Clearely in the Scriptures.”, in Christian Moderation. […], London: […] Miles Flesher [and Richard Oulton?], and are to be sold by Nathaniel Butter, →OCLC, 2nd book (Of Moderation in Matter of Iudgement), page 47

      Their music is employed in celebrating their own criminal exploits, and their discourse in sounding the unfathomable depths of fate, freewill, and foreknowledge.

      1711 March 5 (Gregorian calendar), [Joseph Addison], “THURSDAY, February 23, 1710–1711”, in The Spectator, number 309; republished in Alexander Chalmers, editor, The Spectator; a New Edition, […], volume IV, New York, N.Y.: D[aniel] Appleton & Company, 1853, →OCLC, page 42

      Juſt the Blovv, and juſter ſtill, / Becauſe imbitter'd to me by that Hand / I moſt deteſt; vvhich gives my Soul an Earneſt / Of vaſt unfathomable VVoes to come, / That dreadful Dovv'ry for my dreadful Love.

      1719 March 18 (first performance; Gregorian calendar), Edward Young, Busiris, King of Egypt. A Tragedy. […], London: […] J[acob] Tonson, […], published 1719, →OCLC, Act V, page 61

      [W]hat VVords ſuffice / Thy countleſs Attributes to ſhovv: / Unfathomable Depths Thou [God] art!

      1739, John Wesley, Charles Wesley, “God’s Greatness. From the Same [German].”, in Hymns and Sacred Poems, London: […] William Strahan; and sold by James Hutton, […]; and at Mr. Bray’s, […], →OCLC, part II, stanza I, page 161

      And the sweet peace of joy did almost fill / The depth of her unfathomable look;— […]

      1817 December (indicated as 1818), Percy B[ysshe] Shelley, “Canto Sixth”, in Laon and Cythna; or, The Revolution of the Golden City: A Vision of the Nineteenth Century. […], London: […] [F]or Sherwood, Neely, & Jones, […]; and C[harles] and J[ames] Ollier, […]; by B[uchanan] M‘Millan, […], →OCLC, stanza XXXVIII, page 147

      Synonyms: bottomless, fathomless, impenetrable, unintelligible, abstruse, Chinese, dense, enigmatic · Antonyms: explicable, fathomable, intelligible, penetrable, understandable, apprehensible, clear, limpid