ascorbic acid vs antioxidant

ascorbic acid and antioxidant both are nouns.

Word	Noun	Adjective	Verb	Adverb
ascorbic acid	Yes	No	No	No
antioxidant	Yes	No	No	No

As nouns, antioxidant is a hypernym of ascorbic acid; that is, antioxidant is a word with a broader meaning than ascorbic acid:

ascorbic acid: a vitamin found in fresh fruits (especially citrus fruits) and vegetables; prevents scurvy
antioxidant: substance that inhibits oxidation or inhibits reactions promoted by oxygen or peroxides

Other hypernyms of ascorbic acid include water-soluble vitamin.

ascorbic acid (noun)	antioxidant (noun)
a vitamin found in fresh fruits (especially citrus fruits) and vegetables; prevents scurvy	substance that inhibits oxidation or inhibits reactions promoted by oxygen or peroxides