psi

Meanings

1. The twenty-third letter of Classical and Modern Greek and the twenty-fifth letter of Old and Ancient Greek.
2. A form of psychic energy.

1. Pound per square inch (an imperial unit of pressure)

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

1. Initialism of Policy Studies Institute, a British think tank.

Etymology

From Middle English psi, from Latin psī, from Ancient Greek ψεῖ (pseî), the name for the twenty-third letter of the alphabet (Ψ, ψ).