frustrate, thwart, foil, baffle, balk mean to check or defeat another's plan or block achievement of a goal. frustrate implies making vain or ineffectual all efforts however vigorous or persistent.

FOIL definition: 1. a very thin sheet of metal, especially used to wrap food in to keep it fresh: 2. a piece of a…. Learn more.

FOIL definition: to prevent the success of; frustrate; balk. See examples of foil used in a sentence.

One that stands in contrast to and emphasizes the distinctive characteristics of another: "I am resolved my husband shall not be a rival, but a foil to me" (Charlotte Brontë).

Look up foil in Wiktionary, the free dictionary.

FOIL meaning: 1 : to prevent (someone) from doing something or achieving a goal defeat often used as (be) foiled; 2 : to prevent (something) from happening or being successful

As a verb, if you foil someone's plans or attempts to do something, you cause them to fail. Your brother will be really mad if you foil his plans to hide his mediocre report card from your parents.