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per square inch

sometimes used in paintball
when using or playing paintball and HPA *high pressure air* their could be 850 psi in a pb tank
by viva la vidaa May 06, 2009
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Common abbrevation for Psionic Energy,
it can also be used as the name of a catagory of skills, often called Psionics.
When you make a PsiBall, you can feel the Psi running through your body.

How long have you been doing Psi?
by PsiZero November 06, 2003
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The letter in the Greek Alphabet that comes after chi and before omega.
alpha, beta, gamma, delta, epsilon, zeta, eta, theta, iota, kappa, lambda, mu, nu, xi, omicron, pi, row, sigma, tau, upsilon, phi, chi, psi, omega
by The Cobbgoblin May 16, 2006
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Pounds per square inch.

If used in the form "That person has a high PSI". It is a sexual reference saying there ass or another part of the body where a penis can be inserted is capable of taking alot of pressure, or quite a hard pounding. Can also reference to the largest penis they can fit in their ass before the pressure gets to high and rips it.
That h0 has a really high max psi.
by Anonymous February 24, 2003
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A sex ed program in public school in which teachers who probably haven't actually had sex in about 20 years teach you to keep your hands and other parts to yourself. Sometimes guy will get lucky and have a hot PSI teacher, which makes for an interesting experience.
"Damn, we've got PSI today!"
by Losti March 21, 2005
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When you pretend you dont know someone even though you folow them on twitter this is what you call them
Jake Paul: who is PSI CSI KSI ETC.
by pake paul February 25, 2018
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