1.  celeriac(n = noun.plant) apium graveolens rapaceum, celery root, knob celery, root celery, turnip-rooted celery - grown for its thickened edible aromatic root;
is a kind of herb, herbaceous plant
has parts: celeriac, celery root

2.  celeriac(n = noun.food) celery root - thickened edible aromatic root of a variety of celery plant;
is a kind of root vegetable
is a part of apium graveolens rapaceum, celeriac, celery root, knob celery, root celery, turnip-rooted celery

   Turnip-rooted celery, a from of celery with a large globular root, which is used for food. [1913 Webster]

celeriac, n. a variety of celery with a swollen turnip-like stem-base used as a vegetable.

Etymology:
CELERY: -ac is unexplained