Definitions
1.nounThe eighth letter of the Modern Greek alphabet, ninth in Old Greek: Θ, θ.
2.nounThe measure of an angle.
3.nounThe sensitivity of the value of a derivative with respect to time; the "time decay".
4.nounDesignating 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.nounThe voiceless dental fricative represented by θ.