The Greek capital letter psi is often used to represent the word, or study of, Psychology.
For example:
Ψ = Psychology
Ψist = Psychologist.
Ψ, in biological terms, is a symbol used to represent water potential.
Ψ, in astrology, is the symbol that represents Neptune.

Ψ, in physics, is the symbol used to represent the quantum-mechanical wave-function.
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