Webster's Revised Unabridged Dictionary · 1913

Pisces

Pisces , noun, plural

[Latin piscis a fish.]

1.
(a) (Astronomy) The twelfth sign of the zodiac, marked P in almanacs.
(b)
(Astronomy) A zodiacal constellation, including the first point of Aries, which is the vernal equinoctial point; the Fish.
2.
(Zoology) The class of Vertebrata that includes the fishes. The principal divisions are Elasmobranchii, Ganoidei, and Teleostei.