BOOM, noun A long pole or spar, run out from various parts of a ship, or other vessel, for the purpose of extending the bottom of particular sails; as the jib-boom, studding-sail boom main-boom, square-sail boom etc.
1. A strong iron chain, fastened to spars, and extended across a river, or the mouth of a harbor, to prevent an enemy's ships from passing.
2. A pole set up as a mark to direct seamen how to keep the channel, in shallow water.
BOOM, verb intransitive
1. In marine language, to rush with violence, as a ship under a press of sail.
2. To swell; to roll and roar, as waves.
The hoarse waves booming to the ocean shore.
3. To cry as the bittern.
The Dutch use bom for the sound of an empty barrel, and bommen is to drum.