Originally: a fish of the former genus Panchax of small Old World tropical killifishes (family Poeciliidae); (in form Panchax) the genus itself. In later use more widely: any of numerous killifishes, especially of the genus Aplocheilus, and including many popular aquarium species.
Members of the former genus Panchax are now included in Aplocheilus.
Early 19th century. From scientific Latin panchax, specific name, later also a former genus name, of uncertain origin; perhaps from ancient Greek πάγχυ wholly, entirely (ultimately from πάς all, although the suffixation is unclear); apparently so called on account of the entirety of the tail fin.