1. Marked by a lack of responsibility: irresponsible accusations.
2. Lacking a sense of responsibility; unreliable or untrustworthy.
3. Law. Not mentally or financially fit to assume responsibility.
4. Not liable to be called to account by a higher authority.

1. One who has no sense of responsibility.
2. Law. One who is mentally or financially unfit to assume responsibility for one's actions.
3. One who is unlikely to be called to account by a higher authority.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.