- [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.
- [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.
- A pole with a conspicuous top, set up to mark the channel in a river or harbor.(Obs)
- [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.
- [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.
Etymology: D. boom tree, pole, beam, bar. See Beam