- Noun. (countable) Anything that seems to be something that it is not.
- Noun. (countable) A misapprehension; a belief in something that is in fact not true.
- Noun. (countable) A magician’s trick.
- Noun. (uncountable) The fact of being an illusion (in any of the above senses). (rfex, this is totally unclear to me) .