BOOM, a pole, bar or barrier (cf. Ger. Baum, tree, Eng. beam) ; applied as a nautical term to a long spar used to extend a sail at the foot (main-boom, jib-boom, etc.). In the sense of a barrier, a boom is generally formed of timber lashed together, or of chains, built across the mouth of a river or harbour as a means of defence. The "boom" of a cannon, the cry of the bittern, etc., is a different and onomatopoeic word.
In trade, the word boom has two applications. First, it is used colloquially as the equivalent of to push or to advertise energeti cally; to carry through with a rush and a roar. Hence, no doubt, the derivation from boom, a loud roar or rumble, as in the boom of a gun, boom being a word imitative of the sound it describes. In this sense of booming a thing by sounding its merits, the origin was American. In 1878 Mr. J. B. McCullagh, according to his own statement to The Century Dictionary used the term in the Grant presidential campaign through his familiarity with its use by Mississippi pilots to describe the rapid swelling and rising of the river. So he came to speak of the Grant campaign as "booming," and the term passed into general English-speaking use.
In a second sense, the word "boom" is commonly applied to the peak of a trade cycle as opposed to its lowest point which is often called the slump : the two words are now in common use as an expressive pair of antithetical terms.