noun The eighth letter of the Modern Greek alphabet, ninth in Old Greek: Θ, θ.
noun The measure of an angle.
noun Pitch angle; the angle between an aircraft's longitudinal axis and the horizontal plane.
noun The sensitivity of the value of a derivative with respect to time; the "time decay".
noun 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).
noun The voiceless dental fricative represented by θ.