noun
psi
pseye
noun
1
The 23rd letter of the Greek alphabet (Ψ, ψ).
"Psi comes near the end of the Greek alphabet, just before omega."
2
In parapsychology, a supposed form of psychic or mental energy behind ESP and similar phenomena.
"The novel treats psi as a real, measurable force some characters can channel."
symbol
1
Abbreviation for "pounds per square inch," a unit of pressure.
"The tyre should be inflated to about 32 psi."
How to Use Psi
Learner’s notesIn plain EnglishEither the Greek letter, or (informally) mental/psychic energy, or the pressure unit "pounds per square inch."
Common mistake
Context decides the meaning — psi in a maths equation is the letter, psi in a tyre gauge is pressure, and psi in a sci-fi story is psychic power.
Common pairings
measured in psi
psi rating
psychic psi
Word Forms
psis plural
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_____ comes near the end of the Greek alphabet, just before omega.
Etymology
From the Greek letter name psi (Ψ), going back to Ancient Greek psei.