Eel n. : An elongated fish of many genera and species. The common eels of Europe and America belong to the genus Anguilla. The electrical eel is a species of Gymnotus. The so called vinegar eel is a minute nematode worm. See Conger eel, Electric eel, and Gymnotus.

Example:
How would a fire Eel do in a planted aquarium?

Taxonomy
Eel, Anguilliformes, Suborders, snake, FishBase, family, free encyclopedia, fish, freshwater eels, delicacy, cognate, Hittite, smoked eel, Europe, larvae, moray eel, Old High German, electric eels.

Defination from the web:
... The term "eel" is also used for some other similarly shaped fish, such as electric eels and spiny eels, but these are not members of the Anguilliformes order. ...