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psi

or p.s.i

1.
pounds per square inch.

psi1

[sahy, psahy] /saɪ, psaɪ/
noun, plural psis.
1.
the 23rd letter of the Greek alphabet (Ψ, ψ).
2.
the group of consonant sounds represented by this letter.
Origin of psi1
1350-1400
1350-1400; Middle English < Greek pseî

psi2

[sahy] /saɪ/
noun
1.
any purportedly psychic phenomenon, as psychokinesis, telepathy, clairvoyance, or the like.
Origin
1940-45; shortening of psychic or parapsychic
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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British Dictionary definitions for psi

psi1

abbreviation
1.
pounds per square inch

psi2

/psaɪ/
noun
1.
the 23rd letter of the Greek alphabet (Ψ, ψ), a composite consonant, transliterated as ps
2.
  1. paranormal or psychic phenomena collectively
  2. (as modifier): psi powers
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for psi
n.

23rd letter of the Greek alphabet. Use for "psychic force, paranormal phenomenon" dates from 1942 (probably from psychic (adj.)).

Online Etymology Dictionary, © 2010 Douglas Harper
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psi in Medicine

psi 1 (sī, psī)
n.

Symbol ψ The 23rd letter of the Greek alphabet.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Word Value for psi

5
6
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