theta

1. (mathematics) The measure of an angle.

2. (aviation, by extension) Pitch angle; the angle between an aircraft's longitudinal axis and the horizontal plane.Synonyms: deck anglebroadly

3. (finance) The sensitivity of the value of a derivative with respect to time; the "time decay".

4. (biology) 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).Examples: "The reader is less likely to throw the book down in a fit of disgust than she is to be lulled into a theta state, a highway hypnosis induced by page after page of incantatory prose."

5. (phonology) The voiceless dental fricative represented by θ.