'sialorrhea' originates from New Latin/medical formation, built from Greek elements: 'sialo-' (from Greek 'sialon') and '-rrhea' (from Greek 'rhēa'), where 'sialo-' meant 'saliva' and 'rhēa' meant 'a flowing or discharge'.

'sialorrhea' was formed in medical New Latin and entered English as a technical/medical term. Earlier English medical usage sometimes preferred the related term 'ptyalism' (from Greek 'ptyalon', 'saliva'), but 'sialorrhea' became the standard formation using the '-rrhea' suffix for abnormal flow or discharge.

Initially and historically it has meant 'excessive flow or discharge of saliva'; this core meaning has been retained in modern medical usage.