knob celery vs root celery

knob celery and root celery both are nouns.

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

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

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

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

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