Real Dictionary

psi in American English 1
the twenty-third letter of the Greek alphabet (Ψ, ψ)
noun: the 23rd letter of the Greek alphabet (Ψ, ψ)

psi in American English 2
of or having to do with psychic or paranormal abilities or phenomena
such abilities or phenomena collectively
noun: any purportedly psychic phenomenon, as psychokinesis, telepathy, clairvoyance, or the like

psi in American English 3
abbreviation: pounds per square inch

psi in British English 1
abbreviation for: pounds per square inch

psi in British English 2
noun: the 23rd letter of the Greek alphabet (Ψ, ψ), a composite consonant, transliterated as ps