Boom meaning : A low-pitched, resonant sound, such as of an explosion. A rapid expansion or increase. One of the calls of certain monkeys or birds. To make a loud, hollow, resonant sound. (of speech) To exclaim with force, to shout, to thunder. To make something boom. To publicly praise. To rush with violence and noise, as a ship under a press of sail, before a free wind. Used to suggest the sound of an explosion. Used to suggest something happening suddenly and unexpectedly.