We found 10 dictionaries that define the word optical illusions:

General (7 matching dictionaries)

1. optical illusions: Merriam-Webster
2. optical illusions: Collins English Dictionary
3. optical illusions: Vocabulary.com
4. optical illusions: Cambridge Advanced Learner's Dictionary
5. optical illusions: Wiktionary
6. Optical illusions: Wikipedia, the Free Encyclopedia
7. Optical illusions: TheFreeDictionary.com

Medicine (2 matching dictionaries)

8. Medical Dictionary (No longer online)
9. online medical dictionary (No longer online)

Slang (1 matching dictionary)

10. Optical illusions: Street Terms: Drugs and the Drug Trade

(Note: See optical_illusion as well.)

Definitions from Wiktionary (optical illusion) ▸ noun:  An image that is visually deceptive or misleading. ▸ Also see optical_illusion ▸ Words similar to optical illusions ▸ Usage examples for optical illusions ▸ Idioms related to optical illusions ▸ Wikipedia articles (New!) ▸ Words that often appear near optical illusions ▸ Rhymes of optical illusions ▸ Invented words related to optical illusions