eel vs conger eel

eel and conger eel both are nouns.

Word	Noun	Adjective	Verb	Adverb
eel	Yes	No	No	No
conger eel	Yes	No	No	No

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

eel: voracious snakelike marine or freshwater fishes with smooth slimy usually scaleless skin and having a continuous vertical fin but no ventral fins
conger eel: large dark-colored scaleless marine eel found in temperate and tropical coastal waters; some used for food

Other hyponyms of eel include elver, common eel, freshwater eel, Anguilla sucklandii, tuna, moray, moray eel, conger.

eel (noun)	conger eel (noun)
voracious snakelike marine or freshwater fishes with smooth slimy usually scaleless skin and having a continuous vertical fin but no ventral fins	large dark-colored scaleless marine eel found in temperate and tropical coastal waters; some used for food
the fatty flesh of eel; an elongate fish found in fresh water in Europe and America; large eels are usually smoked or pickled