diarrheal

The word 'diarrheal' is built upon the core noun 'diarrhea', which originates from the Greek 'diarrhoia', itself a compound of 'dia-' (through) and '-rrhoia' (flowing, discharge). This literal sense of "a flowing through" perfectly describes the physiological condition. The suffix '-al', of Latin origin via French, is then appended to form the adjective, shifting the meaning to "pertaining to or characterized by such a flow". Thus, the modern medical term retains the vivid, descriptive logic of its ancient Greek components, directly linking the symptom to its etymological roots.