Synonyms and related words :
accidental, adventitious, agnostic, aleatory, ambiguous, capricious, casual, causeless, chance, chancy, changeable, contingent, destinal, dicey, doubting, equivocal, erratic, extraordinary, fatal, fatidic, fickle, fluky, fortuitous, hesitant, hesitating, iffy, improbable, incalculable, incidental, indecisive, indemonstrable, indeterminate, irresolute, more than expected, out-of-the-way, past expectation, polysemous, risky, skeptical, sudden, touch-and-go, unaccountable, unannounced, unanticipated, uncaused, uncertain, unconfirmable, unconvinced, undetermined, undivinable, undivined, unexpected, unforeseen, unguessed, unheralded, unhoped for, unlooked-for, unpersuaded, unpredictable, unpredicted, unprepared for, unprovable, unsure, unverifiable, variable, wavering, whimsical, without warning