- (countable) The twenty-third letter of Classical Greek, Classical and Modern Greek and the twenty-fourth letter of Old Greek, Old and Ancient Greek.
- (uncountable) A form of psychic energy.
- 1993, "Come, lad," he said. "We will take tea together and speak of the noumenon, the and other more heterogenous phenomena." " Will Self, My Idea of Fun
- Letter of the Greek alphabet: '''Î¨ Ïˆ
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- French: psi
- French, psi
- Italian: psi
Etymology: Greek , the name for the twenty-third letter of the alphabet (, ).
- Pounds per square inch (an imperial unit of pressure)
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