fast, swiftly, rapidly, speedily, at high speed, with all speed, at (full) speed, at the speed of light, at full tilt, as fast as one's legs can carry one, at a gallop, briskly, at the double, post-haste, with all possible haste, like a whirlwind, like an arrow from a bow, at breakneck speed, expeditiously, madly, hotfoot, with dispatch

informal double quick, in double quick time, p.d.q. (pretty damn quick), nippily, like (greased) lightning, hell for leather, at warp speed, like mad, like crazy, like blazes, like the wind, like a bomb, like nobody's business, like a scalded cat, like the deuce, a mile a minute, like a bat out of hell, like a bullet out of a gun

British informal like the clappers, at a rate of knots, like billy-o

North American informal lickety-split

literary apace

immediately, directly, at once, now, straight away, right away, instantly, forthwith, as soon as possible, shortly, without delay, without further/more ado, instantaneously, expeditiously, suddenly, abruptly;

soon, soon after, promptly, early;

North American momentarily

informal like a shot, a.s.a.p. (as soon as possible), pronto, before you can say Jack Robinson, before the ink is dry on the page, before you can say knife, straight off

archaic straight, instanter

briefly, fleetingly, briskly;

hastily, in haste, precipitately, hurriedly, in a hurry, cursorily, perfunctorily, superficially, desultorily