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foil 1 (foil)
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tr.v. foiled, foil·ing, foils
1. To prevent from being successful; thwart: The alarm system foiled the thieves' robbery attempt.
2. To obscure or confuse (a trail or scent) so as to evade pursuers.
n.
Archaic
1. A repulse; a setback.
2. The trail or scent of an animal.

[Middle English foilen, to trample, defile, variant of filen, to defile; see FILE3.]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2016 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 
foil 2 (foil)
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n.
1. Metal that has been formed into a thin, flexible sheet: aluminum foil.
2. A thin layer of polished metal placed under a displayed gem to lend it brilliance.
3. 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).
4. The reflective metal coating on the back of a glass mirror.
5. Architecture A curvilinear, often lobelike figure or space formed between the cusps of intersecting arcs, found especially in Gothic tracery and Moorish ornament.
6.
a. An airfoil.
b. Nautical A hydrofoil.
tr.v. foiled, foil·ing, foils
1. To cover or back with foil.
2. To wrap (strands of hair) in pieces of foil in order to isolate them after bleach or color has been applied.
3. To set off by contrast.

[Middle English, from Old French foille, from Latin folia, pl. of folium, leaf; see bhel-3 in the Appendix of Indo-European roots.]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2016 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 
foil 3 (foil)
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n.
1. A fencing sword having a usually circular guard and a thin, flexible four-sided blade with a button on the tip to prevent injury.
2. often foils The art or sport of fencing with such a sword: a contest at foils.

[Origin unknown.]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2016 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 

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