Foolproof/ˈfuːlpruːf/ Definition 1 of 1Pro Tip 1/3Error-proof Use 'foolproof' for methods that leave no room for error. He installed a foolproof security alarm at home. Pro Tip 2/3User-Friendly Describe processes or items that are extremely easy to use. The cake mix is foolproof — just add water. Pro Tip 3/3Confidence Inspiring Show that something gives people confidence because it's less likely to go wrong. Her foolproof reputation made her the favorite candidate.