Meaning: Apprehension concerning a planned commitment
Originated in: 🇩🇪 German Confederation
Earliest attestation: Seed-time and Harvest by Fritz Reuter (1862)
To get cold feet about an event or action means to be nervous about it to the point where you consider not going through with it. The stereotypical case is with a wedding where the bride, after months’ of engagement, starts having second thoughts the day of the actual wedding. It can also be used as just a general term of cowardice however.
This idiom allegedly derives from an excuse to stop gambling. After losing everything, even their shoes, people would say they had to stop because of their cold feet now and had to go home to warm them up, not wanting to admit that they had nothing left. Thus they could flee without losing face. It then morphed to a general expression of cowardice before its usage was narrowed again specifically to fear before a big action.
The term is also fitting for the reality of our biological flight-or-flight response. As one gets nervous about an upcoming major decision, the anxiety activates his sympathetic nervous system. This causes vasoconstriction, ensuring blood gets to the muscles where it’s really needed for survival instead of “unimportant” places like your hands, stomach, or feet. Thus, while the saying is idiomatic, in that it isn’t just saying you need to put on socks or something, it does inadvertently reflect a fact of life.