The Collaborative International Dictionary of English v.0.48:

Unplumbed \Unplumbed\
   See plumbed.

WordNet (r) 3.0 (2006):

unplumbed
    adj 1: situated at or extending to great depth; too deep to have
           been sounded or plumbed; "the profound depths of the
           sea"; "the dark unfathomed caves of ocean"-Thomas Gray;
           "unplumbed depths of the sea"; "remote and unsounded
           caverns" [syn: profound, unfathomed, unplumbed,
           unsounded]

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "unplumbed":
   able, all-comprehensive, all-inclusive, boundless, countless,
   endless, enigmatic, eternal, exhaustless, extending everywhere,
   illimitable, illimited, immeasurable, immense, incalculable,
   incognizable, incomprehensible, inexhaustible, infinite,
   infinitely continuous, innumerable, interminable, interminate,
   limitless, measureless, mysterious, no end of, perpetual, puzzling,
   sealed, shoreless, strange, sumless, termless, unapparent,
   unapprehended, unascertained, unbeknown, unbounded, uncharted,
   uncircumscribed, unclassified, undisclosed, undiscoverable,
   undiscovered, undivulged, unexplained, unexplored, unexposed,
   unfamiliar, unfathomable, unfathomed, unheard, unheard-of,
   unidentified, uninvestigated, universal, unknowable, unknown,
   unlimited, unmeasurable, unmeasured, unnumbered, unperceived,
   unrevealed, unsuspected, untold, untouched, virgin, without bound,
   without end, without limit, without measure, without number