Synonyms and related words :
abrupt, accidental, adventitious, aleatory, casual, causeless, chance, chancy, contingent, destinal, dicey, electrifying, extraordinary, fatal, fatidic, fluky, fortuitous, hasty, headlong, iffy, impetuous, improbable, impulsive, incidental, indeterminate, more than expected, nerve-shattering, out-of-the-way, past expectation, precipitant, precipitate, precipitous, quick, risky, shocking, speedy, startling, sudden, surprising, swift, unannounced, unanticipated, uncaused, undetermined, undivined, unexpected, unforeseeable, unforeseen, unguessed, unheralded, unhoped for, unpredictable, unpredicted, unprepared for, without warning