Slang One that is uncontrolled and therefore poses danger: "[His] bloopers in the White House seem to make him . . . a political loose cannon” ( Tom Morgenthau). (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.