cold feet, get - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Also, have cold feet. Retreat from an undertaking; lose one's nerve. For example, I got cold feet when I learned the trip involves white-water rafting, or Don't count on including her—she's been known to have cold feet in the past. The origin of this term has been lost. In early 17th-century Italy it meant to be short of money, but that sense has never been used in English. [Late 1800s]