v. 1
To prevent (something) from being accomplished.
v. 2
To blunt; to dull; to spoil.
n. 1
Thin aluminium/aluminum (or, formerly, tin) used for wrapping food.
wrap the sandwich up in foil

Related words

Phrases: aluminium foil tin-foil silver foil aluminum foil foil razor foil shaver

Forms

thwart A moat was dug around the castle to thwart attackers.
disconcert I don't mean to disconcert you, but there's a spider in your hair.
discomfit Don't worry. Your joke did not really discomfit me.
stain I tried washing the shirt, but the stain remained.

Use in printed books, per decade from 1850 to 2019.

3 letters: mar¹
4 letters: file¹, ruin², blot¹, balk¹, bilk¹
5 letters: cross¹, upset², sword¹, spoil¹, queer¹, stain¹, smear¹, evade², sully², elude², botch¹, baulk, spoor¹
6 letters: defeat², scotch¹, hinder², thwart¹, baffle², rapier³, befile
7 letters: setting², disrupt², airfoil², scupper², vitiate³, deprave²
8 letters: contrast², enhancer³, aerofoil
9 letters: frustrate², hydrofoil³, discomfit
10 letters: background², disappoint³, counteract³, circumvent³, disconcert³
11 letters: contaminate⁴
12 letters: transparency⁴

The small number after each word is its number of syllables (ruin² = 2 syllables).