roundworm vs wheat eel

roundworm and wheat eel both are nouns.

Word	Noun	Adjective	Verb	Adverb
roundworm	Yes	No	No	No
wheat eel	Yes	No	No	No

As nouns, wheat eel is a hyponym of roundworm; that is, wheat eel is a word with a more specific, narrower meaning than roundworm:

roundworm: unsegmented worms with elongated rounded body pointed at both ends; mostly free-living but some are parasitic
wheat eel: small roundworm parasitic on wheat

roundworm (noun)	wheat eel (noun)
unsegmented worms with elongated rounded body pointed at both ends; mostly free-living but some are parasitic	small roundworm parasitic on wheat
infections of the skin or nails caused by fungi and appearing as itching circular patches