a word of Teutonic origin (cf. the Ger. Baum, tree, and the Eng. beam) for a pole, bar or barrier, used especially as a nautical term, for a long spar, used to extend a sail at the foot (main-boom, jib-boom, &c.). The "boom" of a cannon (note of a bell, cry of the bittern) is distinct from this, being onomatopoeic. 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. Possibly from the metaphor of a breaking boom, and the accompanying rush and roar, or from the rush of rising waters (mingled with the onomatopoeic use), "boom" began in America to be used of a sudden "spurt" or access of industrial activity, as in the phrase "a boom in cotton." Hence the verb "to boom," meaning to advertise or push into public favour.