noun

psi

PSYE/psaɪ/

The twenty-third letter of the Greek alphabet.

The Greek alphabet places psi between chi and omega.

A single plain alphabet practice card bearing uppercase Ψ and lowercase ψ side by side, making the Greek letter itself the unmistakable subject.

Etymology

Psi names the twenty-third letter of the Greek alphabet. The supplied evidence establishes this use but does not explain the origin of the letter’s name.

In context

Curt Jaimungal9:16

where psi-bar is the Dirac adjoint of psi,

The Story of Geometric Unity

More examples

Lowercase psi is written ψ.
She practices writing uppercase psi, Ψ, on the board.
The equation uses psi to represent a wave function.

Forms

psi · psis