The eighth letter of the Modern Greek alphabet, ninth in Old Greek: Θ, θ. / (mathematics) The measure of an angle.

(US, colloquial) A member of the Kappa Alpha Theta sorority.

plural of theta

A form of meditation and relaxation that is supposed to induce theta waves in the brain.

plural of theta pinch

(physics) A pinch (magnetic compression of an electrically-conducting filament) where the magnetic field runs down the axis of the cylinder, while the electric field is in the azimuthal direction.

(grammar, especially transformational grammar) Abbreviation of thematic role.

The P.3 strain of the SARS-CoV-2 virus that causes COVID-19.

A type of electrical activity in the brain; a brain wave with a frequency of 4-8 hertz.

A type of electrical activity in the brain: brain waves with a frequency of 4-8 hertz.