1. Either of two spongy, saclike respiratory organs in most vertebrates, occupying the chest cavity together with the heart and functioning to remove carbon dioxide from the blood and provide it with oxygen.
2. A similar organ in some invertebrates, including spiders and terrestrial snails.

at the top of (one's) lungs

1. As loudly as one's voice will allow.

[Middle English lunge, from Old English lungen, lungs.]

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.