Celeriac

A variety of celery plant grown for its thick, bulbous root that is eaten as a vegetable; also called celery root or knob celery.

From 'celery' (ultimately from Greek 'selinon') combined with the suffix '-iac' (meaning a person or thing affected by something). The suffix choice is unusual; 'celeriac' literally suggests 'one affected by celery' and was coined in 19th-century English.