1. A long pole or spar, run out for the purpose of extending the bottom of a particular sail; as, the jib boom, the studding-sail boom, etc.
2. (Science: mechanics) a long spar or beam, projecting from the mast of a derrick, from the outer end of which the body to be lifted is suspended.
3. A pole with a conspicuous top, set up to mark the channel in a river or harbor.
4. (Science: astronomy) a strong chain cable, or line of spars bound together, extended across a river or the mouth of a harbor, to obstruct navigation or passage.
5. A line of connected floating timbers stretched across a river, or inclosing an area of water, to keep saw logs, etc, from floating away. Boom iron, one of the iron rings on the yards through which the studding-sail booms traverse. The booms, that space on the upper deck of a ship between the foremast and mainmast, where the boats, spare spars, etc, are stowed.
Origin: D. Boom tree, pole, beam, bar. See beam.