(countable) Anything that seems to be something that it is not. / (countable) A misapprehension; a belief in something that is in fact not true. / (countable) A magician’s trick.

plural of illusion

Under an illusion; deceived.

Subject to or pertaining to an illusion, often used in the sense of an unrealistic expectation or an unreachable goal or outcome.

In a illusive fashion.

The quality of being illusive; deceptiveness; false show.

An image that is visually deceptive or misleading.

plural of optical illusion

An optical illusion whereby a disk appears smaller if surrounded by larger disks than if by smaller.

The optical illusion whereby the moon looks larger when it is low in the sky than otherwise.