I have heard that the names for the months of the year are not from the Torah but rather were acquired during one of the exiles, so that Nissan is not the ‘real’ name of the month. What then is the Torah’s name for the month that Passover is in, and what is the significance of the different names?
The Torah refers to the month that has become to be called Nissan as “haChodesh haRishon” or the first or head of the months. This is because it is always to be reckoned as the first of the months of the year, and all other months are referred to by their position relative to it, i.e., the second, third, fourth etc. By referring to this month as the first we are reminded of the great miracles of the Exodus that occurred in it, as does our reference to each consecutive month recall that event. This is similar to the Torah’s referring to the days of the week by number culminating in the Sabbath such that the “name” of each day actually elevates the status of the seventh. Consequently, we don’t reckon the months according to where they come in the year — recall that the year begins with Rosh Hashanah in Tishrei, which is the seventh month — but rather we count them from the month of our deliverance.
The month of Passover is also referred to as “Chodesh haAviv” which means the month of spring, since the Torah requires that the calendar be calibrated such that this month always occurs in the season that the Exodus occurred. The redemption is then celebrated in the time of year when all living things undergo renewal and renaissance, and bounty is abounding in the world. The early commentators suggest a hidden meaning in this name for the month that connects both ideas: “Aviv” is spelled alef-veys; yud-veys. Alef-veys, “av”, means father, a reference to the head; yud-veys according to gematria has a numerical equivalent of twelve. Thus we see a hint that the head of the months occurs in spring.
The name Nissan is Babylonian in origin, its having been brought back with the Jews from their exile in Babylon. However, this name is also connected with the themes of Exodus and spring. Nissan recalls the word “nes” meaning miracle. Also, insofar as it is similar to the word nitzan, which means bud, it recalls spring, regarding which the verse says, “The buds have appeared in the Land” (Song of Songs 2).
The sign of the Zodiac for this month is Aries, a ram. This is because this sign is clearly visible in the stars during this month. It is for this reason that the ancient Egyptians worshipped the ram as a symbol of fertility, proliferation, wealth and power. The Egyptians, whose entire purpose in life was directed toward riches and physical strength thus deified the ram, bowed down to it and worshiped it. Therefore, the Jews, whose lives are to be directed to G-d and His service, were commanded to slaughter the ram at the apex of its power and influence, and bring it as an offering to G-d. To both Israelite and Egyptian the sign of the month was a ram — for the ancient Egyptians it was a symbol of idolatry, but for Israel it is a symbol of the service of G-d.