In case others don't know this, the reason this is abbreviated Ψ (psi) is that Ψ is the first letter of Greek ψευδής 'false, lying', the origin of the prefix ps

In case others don't know this, the reason this is abbreviated Ψ (psi) is that Ψ is the first letter of Greek ψευδής 'false, lying', the origin of the prefix pseudo-.