1. the 23rd letter of the Greek alphabet (Ψ, ψ)
2. a unit of pressure equal to one pound per square inch
Usage: technical
3. psychic phenomena or abilities; extrasensory perception
Usage: informal

Examples

• The Greek letter psi appears in many mathematical formulas.
• The tire pressure should be maintained at 32 psi.
• The water pump operates at 50 psi.
• Some people claim to have psi abilities like telepathy.
• The researcher studied psi phenomena in controlled experiments.
• Psi is often used as a symbol in psychology and physics.