illusion

a false appearance or mistaken perception

Roots

in- / im- (in/into): in, into, within, or on
lud / lus: play, mock, or trick

Other words with the lud / lus root

allusion: an indirect reference
allusive: hinting indirectly at another idea or text
delusion: a fixed false belief or serious mistaken conviction
illusory: seeming real but false or unreliable

Illusion is reality playing a trick on perception.

The calm voice created the illusion that everything was under control.

Illusion is the familiar doorway into lud. Here il- is not the negative prefix; it is in- meaning at or upon before l. The older image is play that becomes mockery or deception.