unfathomable

1 being or seeming to be without limits the unfathomable reaches of space Synonyms bottomless, boundless, endless, fathomless, horizonless, illimitable, immeasurable, immensurable, indefinite, limitless, measureless, unbounded, infinite, unlimitedRelated Words abysmal; countless, incalculable, incomputable, inestimable, innumerable, unmeasured; exhaustless, inexhaustible; extensive, far-flung, immense, vastNear Antonyms fathomable, measurable; depthless, shallow, superficialAntonyms bounded, circumscribed, confined, definite, finite, limited, restricted

2 impossible to understand for some unfathomable reason the family decided to venture out into the blizzard Synonyms impenetrable, incomprehensible, ungraspable, unintelligibleRelated Words abstruse, enigmatic (also enigmatical), esoteric, indecipherable, inscrutable, recondite, unsearchable; cryptic, darkling, deep, mysterious, mystic, oblique, obscure, occult, uncanny; unanswerable, unknowable; baffling, bewildering, confounding, confusing, mystifying, perplexing, puzzling; inconceivable, unimaginable, unthinkableNear Antonyms basic, elemental, elementary, essential, fundamental, rudimentary, underlying; easy, simple; coherent, connected, ordered, orderly, organized, systematic, systematized; clear, cogent, compelling, convincing, lucid, pellucid, perspicuous, plain, straightforwardAntonyms fathomable, intelligible, understandable