vitamin C vs antioxidant

vitamin C and antioxidant both are nouns.

Word	Noun	Adjective	Verb	Adverb
vitamin C	Yes	No	No	No
antioxidant	Yes	No	No	No

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

vitamin C: 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 vitamin C include water-soluble vitamin.

vitamin C (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