Synonyms and related words :
arcane, cabalistic, extraordinary, impenetrable, improbable, inscrutable, more than expected, mystic, numinous, out-of-the-way, past expectation, sudden, unaccountable, unannounced, unanticipated, undivined, unexpected, unforeseeable, unforeseen, unheralded, unhoped for, unknowable, unpredictable, unpredicted, unprepared for, without warning