Noun

(countable) Anything that seems to be something that it is not.

We saw what looked like a tiger among the trees, but it was an illusion caused by the shadows of the branches.

Using artificial additives, scientists can create the illusion of fruit flavours in food.

* 2002 , (The Flaming Lips),

You realize the sun don't go down it's just an illusion caused by the world spinning round.

(countable) A misapprehension; a belief in something that is in fact not true.

Jane has this illusion that John is in love with her.

(countable) A magician’s trick.

(uncountable) The state of being deceived or misled.

Noun

(en noun)

An act or practice intended to deceive; a trick

The whole conversation was merely a deceit .

An act of deceiving someone

* {{quote-book, year=1998, author=Mike Dixon-Kennedy, title=Encyclopedia of Greco-Roman Mythology, page=125, pageurl=http://books.google.com/books?id=2U7okUE3PIcC&pg=PA125

, passage=Upon his return he killed Eriphyle for her vanity and deceit of him and his father. }}

(uncountable) The state of being deceitful or deceptive

* {{quote-book, year=1611, title=King James Bible, chapter=Psalms 10:7

, passage=His mouth is full of cursing and deceit and fraud: under his tongue is mischief and vanity.}}

(legal) The tort or fraudulent representation of a material fact made with knowledge of its falsity, or recklessly, or without reasonable grounds for believing its truth and with intent to induce reliance on it; the plaintiff justifiably relies on the deception, to his injury.