root celery vs knob celery

root celery and knob celery both are nouns.

Word	Noun	Adjective	Verb	Adverb
root celery	Yes	No	No	No
knob celery	Yes	No	No	No

As nouns, root celery and knob celery are synonyms defined as:

root celery and knob celery: grown for its thickened edible aromatic root

Other synonyms of root celery include Apium graveolens rapaceum, celeriac, celery root, turnip-rooted celery.

root celery (noun)	knob celery (noun)
grown for its thickened edible aromatic root	grown for its thickened edible aromatic root