piscis

Piscis, piscis, m., third declension i-stem, genitive plural piscium. The verb beside it is piscor, piscari, "to fish", a deponent, and the agent noun is piscator, the word the Gospels use of the apostles and the reason the papal signet is the anulus piscatoris, the fisherman's ring.

Fish carry weight in this corpus for the obvious reason. The early Christian fish sign rests on an acrostic of the Greek ichthys, not on the Latin word, so piscis itself is doing plain work when you meet it. Romance keeps the noun everywhere: Spanish pez for the live animal and pescado for the one on the plate, French poisson, Italian pesce. English took Pisces and piscine directly; fish is a Germanic cousin of the same ancient root rather than a borrowing from Latin.