Letter of the month-Zayin
The letter of Sivan is Zayin
Zayin has a numerical value of seven, and symbolizes the material plane, which is built on the sevenfold principle, as seen in the seven days of the week, the seven colors of the spectrum, and the seven tones of the musical scale. The seventh of the divine attributes, Malchut or kingdom, symbolizes the realm of action.
As a word, Zayin denotes tools, as in implements of the material technologies of agriculture or war, for the word Zayin can mean weaponry or seen as etmologically related to the word mazon (foodstuff).
For the month of Sivan, this symbol denotes the giving of the Torah, the weapon against one's evil inclination, and the source of spiritual sustenance. On the material plane, we notice that Sivan is the month when wheat is harvested.
-from Above the Zodiac by Matisyahu Glazerson.