psi¹

As a word

• Psi (Cyrillic) (Ѱ, ѱ), a letter of the early Cyrillic alphabet, adopted from Greek
• Psi (Greek) (Ψ, ψ) a letter of the Greek alphabet
• Psi (comics), a character in DC Comics
• Psi (instant messaging client), a popular Jabber client program
• Psi (parapsychology)

As a greek letter

• J/ψ particle, a subatomic particle
• Wavefunction in Quantum Mechanics, ψ
• In mathematics, Ψ is used to denote the angle between the tangent and the x-axis in the intrinsic coordinates system
• Again in mathematics, Ψ is also used to denote the Digamma and Polygamma functions.
• In physical chemistry, Ψ represents Water potential, the potential energy of a water solution relative to pure water.

As an acronym

PSI

PSI can be an abbreviation for:

• Italian Socialist Party (Partito Socialista Italiano)
• Pandemic Severity Index by the US Centers for Disease Control and Prevention
• Paul Scherrer Institute in Villigen, Switzerland
• Pechersk School International in Kyiv, Ukraine.
• Permanent Staff Instructor in the British Army
• Permanent Subcommittee on Investigations (PSI) of the US Senate
• Pneumonia severity index
• Pollutant Standards Index, an air pollution index developed by the US Environmental Protection Agency
• Population Services International, an international healthcare NGO based in Washington DC
• Postpartum Support International, 501(c)3 organization devoted to women's mental health issues
• Presentence Investigation
• Professional Secretaries International
• Professors for a Strong Israel
• Program Specific Information, part of the MPEG transport stream protocol. Metadata for digital transmission
• Proliferation Security Initiative
• Public Services International, a global union federation of public sector trade unions
• PSI (computational chemistry) software
• PSI (prion), an infectious protein in yeast
• PSI Records, a record label
• Psi is a common shortening of the word psychic
• Statisticians In The Pharmaceutical Industry, the PSI acronym (rather than SPI) is chosen for its relation to the Greek letter Ψ, commonly used in statistical formulae.

psi

• Pounds per square inch, a unit of pressure

pSi

• Porous silicon

See also

• Psi Power A 1978 song by the UK rock group Hawkwind.

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