theta

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

The measure of an angle.

Pitch angle; the angle between an aircraft's longitudinal axis and the horizontal plane.

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

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).

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.

A member of the Kappa Alpha Theta sorority.