psi 1
/suy, psuy/ , n. , pl. psis .
1. the 23rd letter of the Greek alphabet.
2. the group of consonant sounds represented by this letter.
[ 1350-1400; ME pseî ]
psi 2
/suy/ , n.
any purportedly psychic phenomenon, as psychokinesis, telepathy, clairvoyance, or the like. Cf. pseudoscience, parapsychology .
[ 1940-45; shortening of PSYCHIC or parapsychic ]
pounds per square inch.
Also, p.s.i.