garden pea vs split-pea

garden pea and split-pea both are nouns.

Word	Noun	Adjective	Verb	Adverb
garden pea	Yes	No	No	No
split-pea	Yes	No	No	No

As nouns, split-pea is a hyponym of garden pea; that is, split-pea is a word with a more specific, narrower meaning than garden pea:

Other hyponyms of garden pea include snow pea, sugar pea, sugar snap pea.

garden pea (noun)	split-pea (noun)
fresh pea	dried hulled pea; used in soup
plant producing peas usually eaten fresh rather than dried
the flattened to cylindric inflated multi-seeded fruit of the common pea plant