I. adjective
Synonyms: fast 3, breakneck, fleet, harefooted, hasty, quick, raking, rapid, snappy, speedy
Related Word: headlong, precipitate, sudden; double-quick; supersonic
Antonyms: sluggish
II. adverb
Synonyms: fast 2, flat-out, fleetly, full tilt, promptly, quick, quickly, rapidly, speedily, swiftly
Antonyms: sluggishly