Definition of theta
the eighth letter of the Greek alphabet (Θ, θ), transliterated as ‘th.’.
) [followed by Latin genitive] Astronomy the eighth star in a constellation:Theta Draconis
[as modifier] Chemistry denoting a temperature at which a polymer solution behaves ideally as regards its osmotic pressure. [as modifier] denoting electrical activity observed in the brain under certain conditions, consisting of oscillations having a frequency of 4 to 7 hertz:theta rhythm
) temperature (especially in degrees Celsius).
) a polar coordinate. Often coupled with phi.