fathomless

fathom +‎ -less

fathomless (comparative more fathomless, superlative most fathomless)

1. Very deep (especially of water deeper than a lead line can measure); bottomless, immeasurable.
   • 1865, Walt Whitman, “When Lilacs Last in the Dooryard Bloom’d”, in Sequel to Drum-Taps: When Lilacs Last in the Dooryard Bloom’d and other poems:

     Prais’d be the fathomless universe, / For life and joy, and for objects and knowledge curious, / And for love, sweet love—but praise! praise! praise! / For the sure-enwinding arms of cool-enfolding death.

2. (by extension) unfathomable or incomprehensible.

• (very deep): soundless; See also Thesaurus:deep
• (incomprehensible): ungraspable, unknowable; See also Thesaurus:incomprehensible

• fathomlessly