Feeling nervous or terrified, as in When I looked over the cliff, I broke out in a cold sweat. This expression refers to perspiring accompanied by a feeling of cold, which can be induced by acute fear as well as by fever. [Late 1700s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.