Speed  —n. 1 rapidity of movement. 2 rate of progress or motion. 3 gear appropriate to a range of speeds of a bicycle. 4 photog. A sensitivity of film to light. B light-gathering power of a lens. C duration of an exposure. 5 slang amphetamine drug. 6 archaic success, prosperity. —v. (past and past part. Sped) 1 go or send quickly. 2 (past and past part. Speeded) travel at an illegal or dangerous speed. 3 archaic be or make prosperous or successful.  at speed moving quickly. Speed up move or work faster.  speeder n. [old english]