theta

noun

1. 1

   The eighth letter of the Modern Greek alphabet, ninth in Old Greek: Θ, θ.

2. 2

   The measure of an angle.

3. 3

   The sensitivity of the value of a derivative with respect to time; the "time decay".

4. 4

   Designating a level of brain activity as measured by electroencephalography having a frequency of between four and seven cycles per second (associated with drowsiness in adults).

5. 5

   The voiceless dental fricative represented by θ.