Source : Webster's Revised Unabridged Dictionary (1913)

Celeriac \Ce*le"ri*ac\, n. (Bot.)
   Turnip-rooted celery, a from of celery with a large globular
   root, which is used for food.

Source : WordNet®

celeriac
     n 1: grown for its thickened edible aromatic root [syn: {celery
          root}, {knob celery}, {root celery}, {turnip-rooted
          celery}, {Apium graveolens rapaceum}]
     2: thickened edible aromatic root of a variety of celery plant
        [syn: {celery root}]