sweet basil vs herb

sweet basil and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweet basil	Yes	No	No	No
herb	Yes	No	No	No

As nouns, herb is a hypernym of sweet basil; that is, herb is a word with a broader meaning than sweet basil:

sweet basil (noun)	herb (noun)
leaves of the common basil; used fresh or dried	aromatic potherb used in cookery for its savory qualities
annual or perennial of tropical Asia having spikes of small white flowers and aromatic leaves; one of the most important culinary herbs; used in salads, casseroles, sauces and some liqueurs	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests