Английский Этимологический словарь - boom (n.)

- "long pole," 1543, from Scottish boun, borrowed from Du. boom "tree, pole, beam," from a M.Du. word analogous to O.E. beam. The business sense (1873) is probably from the nautical meaning "a long spar run out to extend the foot of a sail;" a ship "booming" being one in full sail.