psi

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psi / (p)sī/ • n. 1. the twenty-third letter of the Greek alphabet (Ψ, ψ), transliterated as ‘ps.’ ∎  (Psi) [followed by Latin genitive] Astron. the twenty-third star in a constellation: Psi Aquarii.2. supposed parapsychological or psychic faculties or phenomena: he turns to anecdotal evidence to prove that psi exists.

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