N. unintelligibility, incomprehensibility, imperspicuity, inconceivableness, vagueness, obscurity, ambiguity, doubtful meaning, uncertainty, perplexity, spinosity, obscurum per obscurius, mystification, latency, transcendentalism, paradox, oxymoron, riddle, enigma, puzzle, diagnus vindice nodus, sealed book, steganography, freemasonry, pons asinorum, asses' bridge, high dutch, greek, hebrew, jargon

V. be unintelligible, require explanation, have a doubtful meaning, pass comprehension, render unintelligible, conceal, darken, confuse, perplex, not understand, lose, lose the clue, miss, not know what to make of, be able to make nothing of, give it up, not be able to account for, not be able to make either head or tail of, be at sea, wonder, see through a glass darkly, not understand one another, play at cross purposes

Adj. unintelligible, unaccountable, undecipherable, undiscoverable, unknowable, unfathomable, incognizable, inexplicable, inscrutable, inapprehensible, incomprehensible, insolvable, insoluble, impenetrable, illegible, as greek to one, unexplained, paradoxical, enigmatic, enigmatical, puzzling (secret) 533, indecipherable, obscure, dark, muddy, clear as mud, seen through a mist, dim, nebulous, shrouded in mystery, opaque, dense, undiscernible, misty, hidden, latent, indefinite, garbled, perplexed, undetermined, vague, loose, ambiguous, mysterious, mystic, mystical, acroamatic, acroamatical, metempirical, transcendental, occult, recondite, abstruse, crabbed, inconceivable, inconceptible, searchless, above comprehension, beyond comprehension, past comprehension, beyond one's depth, unconceived, inexpressible, undefinable, incommunicable, unpredictable, unforeseeable

Phr. it's greek to me