Vomit, as in When Anne saw the wound, she thought she'd lose her lunch. This expression does not usually refer to a specific meal and probably survives because of alliteration. [Colloquial; c. 1940]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.