(countable) The twenty-third letter of Classical and Modern Greek and the twenty-fifth letter of Old and Ancient Greek. / (uncountable, parapsychology) A form of psychic energy.

Pounds per square inch (an imperial unit of pressure)

Initialism of pre-sentence investigation. / Initialism of protein structure initiative. / Initialism of pollutant safety/standard index (measurement of the air pollutant such as haze)

plural of psi

(anatomy) Initialism of posterior superior iliac spine.

(mathematics) A function of a complex variable obtained by differentiating the logarithm of a gamma function; the digamma function / (physics) The Schrödinger wave function

plural of psi function

(physics) A subatomic particle with an unusually long lifetime and a large mass; a bound state of a charm quark and an anti-charm quark.

plural of J/psi particle

Synonym of J/psi particle