Boom n.
 1. Naut. 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. Mech. 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. [Obs.]
 4. Mil. & Naval 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. Lumbering 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.