The constellations that make up the zodiac are the ones through which the Sun, the Moon, and the other planets travel. The line along which these all travel is known as the ecliptic, and a band of about 4 degrees either side of this contains the zodiacal constellations. The origin of these star signs comes to us from early Babylonian and most probably Sumerian astrology. This band is divided into twelve representing the twelve lunar months. This was adopted, with a few changes, by the Greeks who called it, among other things, kyklos zodiakos, literally, the Circle of Animals, since most of them were animals.

The Sumerians were the eastern neighbours of the Babylonians living in the Mesopotamian valley between the Tigris and Euphrates rivers. They spoke a language isolate, that is, a language that scholars have been unable to link to any other known language. They invented the cuneiform writing system to record this language, and because they wrote on durable clay tablets many have survived until this present day.

The Babylonians spoke a Semitic language (ie related to modern Hebrew, Arabic, Ethiopic, etc.) known as Akkadian. Over time, the Babylonians assimilated the Sumerian culture into their own, borrowing much from the Sumerians. They took to using cuneiform for writing, and they used the Sumerian language itself as a technical and spiritual language, in much the same way that Latin was used in medieval times. Most early Mesopotamian astronomical data that has come down to the present was recorded in Babylonian times, but in the Sumerian language, thus it is not possible to know whether it was of Sumerian or Babylonian origin. Nonetheless it is assumed that the most basic concepts were Sumerian.

By 3000 BC the Sumerians/Babylonians had at least four significant constellations, one to mark each season by its heliacal rising. These were:


Later these were added to and some were split up to make the twelve constellations known today. Follow link to get a detailed etymology:
Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagitarius, Capricorn, Aquarius, Pisces.
Aries From Latin Aries the Ram, translating Greek Krios the Ram, translating Akkadian Immeru the Sheep.
Taurus From Latin Taurus the Bull, from the Greek Tauros the Bull, translating Akkadian Alap-same the Bull-of-Heaven, translating Sumerian Gu.ud an.na the Bull-of-Heaven.
Gemini From Latin Gemini the Twins, translating Greek Didymoi the Twins, translating Akkadian Masu the Great Twins, translating Sumerian Mas.tab.ba gal.gal the Great Twins.
Cancer From Latin Cancer the Crab, translating Greek Karkinos the Crab, translating Akkadian Allutu the Crab, translatin Sumerian Al.lul the Crab.
Leo From Latin Leo the Lion, translating Greek Leon the Lion, translating Akkadian Ka.lab.me.e the Lion, possibly a modification of the Sumerian name Ur.gu.la which may have meant the Great Dog.
Virgo From Latin Virgo the Virgin, translating the Greek Parthenos the Virgin. Akkadian Absinnu the Furrow Sumerian Ab.sin the Furrow
Libra From Latin Libra the Scales, translating the relatively uncommon Greek term, used by Hipparchos, Zygos the Scales. Usually in Greek these stars were known as Chelai the Claws, and were often seen as part of a larger, double sign, Skorpios the Scorpion. However, we must assume that the Greeks knew of the sign as representing a set of scales since the Akkadian name was Zibanitu the Scales, which was a adoption of the Sumerian Zib.ba.anna the Heavenly Weighing Scales.
Scorpio This sign is one of the earliest signs, originally signalling the arival of Autumn to the ancient Mesopotamians. Its name comes to us from Latin Scorpio the Scorpion, from the Greek Skorpios, a translation of the Akkadian Agrabu the Scorpion, itself translating the Sumerian Gir.u.tab the Stinger.
Sagitarius From Latin Sagitarius the Archer, from sagitta an arrow. A translation of the Greek Taxotes the Archer, translating the Akkadian Nedu the Soldier, translating the Sumerian Us the Soldier. Though Sumerian also had the name Pa.bil.sag which may mean, the Archer.
Capricorn Capricorn was called in Latin Capricornus, which is actually an adjective, literally meaning, Goat-Horned. This is a direct translation of the Greek Aigokeros Goat-Horned, from aigos, aix a goat + keros a horn. However, in many of the early representations, and some of the current ones, the sign is drawn as a half-goat, half-fish. This image comes to us from Mesopotamia. The Akkad name Suhu-massa, and the Sumerian name Suhur.mas, both mean the Fish-Goat.
Aquarius This name is from Latin Aquarius the Water-Carrier. This is a noun use of the adjective aquarius pertaining to water. It is a translation og the Greek Hydrochoos the Water-Pourer. The Akkadian name Qu-hasbu may have meant 'streams', and the Sumerian term Gu.la possibly meant 'great man'.
Pisces.
From Latin Pisces the Fish, plural of piscis a fish. A translation of the Greek Ichthyes the Fish, the plural of ichthys a fish. The Akkadians and Sumerians had two names for this constellation. Firstly Akkadian Zibbati and Sumerian Zi.me both meaning the Tails. And Secondly Akkadian Rikis nu.mi and Sumerian Du.nu.nu both which meant the Fishcord. This wouldd account for the common graphic representation of this sign as two fish joined by the tails with a cord.