Welsh rhith

← Proto-Brythonic *rriθ (inherited)

← Proto-Celtic *ɸrixtus (inherited)

← Proto-Indo-European *prep- (inherited)

→ Welsh rhagrith (affix)

→ Welsh rhithweledigaeth (affix)

→ Welsh rhithiol (suffix)

→ Irish riocht (cognate)

→ Ancient Greek πρέπω (cognate)