corn vs sweet corn

corn and sweet corn both are nouns.

Word	Noun	Adjective	Verb	Adverb
corn	Yes	No	Yes	No
sweet corn	Yes	No	No	No

As nouns, sweet corn is a hyponym of corn; that is, sweet corn is a word with a more specific, narrower meaning than corn:

corn: ears of corn that can be prepared and served for human food
sweet corn: corn that can be eaten as a vegetable while still young and soft

Other hyponyms of corn include green corn, hominy, popcorn.

As nouns, sweet corn is a hyponym of corn; that is, sweet corn is a word with a more specific, narrower meaning than corn:

corn: tall annual cereal grass bearing kernels on large ears: widely cultivated in America in many varieties; the principal cereal in Mexico and Central and South America since pre-Columbian times
sweet corn: a corn plant developed in order to have young ears that are sweet and suitable for eating

corn (noun)	sweet corn (noun)
something sentimental or trite	corn that can be eaten as a vegetable while still young and soft
ears of corn that can be prepared and served for human food	a corn plant developed in order to have young ears that are sweet and suitable for eating
whiskey distilled from a mash of not less than 80 percent corn
tall annual cereal grass bearing kernels on large ears: widely cultivated in America in many varieties; the principal cereal in Mexico and Central and South America since pre-Columbian times
(Great Britain) any of various cereal plants (especially the dominant crop of the region--wheat in Great Britain or oats in Scotland and Ireland)
the dried grains or kernels or corn used as animal feed or ground for meal
a hard thickening of the skin (especially on the top or sides of the toes) caused by the pressure of ill-fitting shoes

corn (verb)	sweet corn (verb)
preserve with large-grained rock salt
feed (cattle) with corn