We found 9 dictionaries that define the word theta waves:

General (4 matching dictionaries)

1. theta waves: Oxford Learner's Dictionaries
2. theta waves: Wiktionary
3. Theta waves: Wikipedia, the Free Encyclopedia
4. Theta waves: TheFreeDictionary.com

Business (1 matching dictionary)

5. Theta waves: Legal dictionary

Computing (1 matching dictionary)

6. Theta waves: Encyclopedia

Medicine (3 matching dictionaries)

7. Dorland's Illustrated Medical Dictionary (No longer online)
8. Sleep Terms (No longer online)
9. theta waves: Medical dictionary

(Note: See theta_wave as well.)

Definitions from Wiktionary (theta wave) ▸ noun:  A type of electrical activity in the brain; a brain wave with a frequency of 4-8 hertz. ▸ Also see theta_wave ▸ Words similar to theta waves ▸ Usage examples for theta waves ▸ Idioms related to theta waves ▸ Wikipedia articles (New!) ▸ Words that often appear near theta waves ▸ Rhymes of theta waves ▸ Invented words related to theta waves