sudden (adjective) sudden: unexpected; happening quickly
Sinonime: abrupt,
accelerated,
acute,
expeditious,
fast,
flash,
fleet,
hasty, headlong,
hurried,
immediate,
impetuous,
impromptu,
impulsive, out of the blue, precipitant,
precipitate,
precipitous,
quick, quickened,
rapid,
rash, rushing, spasmodic, speeded, subito,
swift,
unforeseen,
unusualAntonime: expected,
slow