perceptibly Antonyms

imperceptibly abruptly at one stroke in one fell swoop cold turkey on a dime before you know it at the speed of light at warp speed in a blink entirely without warning all at one time all in one go at one fling at a stroke asudden all of the sudden apace briskly directly FAST hastily immediately at once all at once all of a sudden damply observably unnoticeably in a jiff