psi

noun2

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.

   • ‘Come, lad,’ he said. ‘We will take tea together and speak of the noumenon, the psi and other more heterogenous phenomena.’ — 1993

noun3

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