Why is Rosh Chodesh, the holiday that marks the entry of a new Jewish month, considered a "women's holiday"?
Indeed, although the semi-holiday of Rosh Chodesh is celebrated by both men and women, there's a special feminine connection to the day. This expresses itself in the fact that women abstain from certain forms of work on this day—for the details, see How does a Jewish woman celebrate Rosh Chodesh?
The special connection between women and Rosh Chodesh harks way back to the episode of the Golden Calf, when the women declined to participate in the "fundraising" effort and refused to surrender their jewelry for use in making the idol. As a reward, they were given Rosh Chodesh as a day which they observe more than the men (Tur, Orach Chaim 417).
The Rebbe elaborates on this a bit, and explains that the women's non-participation stemmed from their greater faith. Though they had just spent more than two centuries in idolatry-steeped Egypt, a fact that explains why the men caved so quickly at the hint of trouble, the women's faith remained unshakable, and they considered the idea of making an idol totally unthinkable.
The Rebbe continues to explain that all of Judaism is based on this strong faith, and though faith at times can become "fuzzy," it is the women who, in every situation, remain steadfast in this faith and pass it on to their children—the future generations (see Likutei Sichot vol. 8 pg. 315ff).
Perhaps this explains the special connection to Rosh Chodesh. Rosh Chodesh celebrates the monthly renewal of the moon, after it wanes to the point of disappearance. Thus Rosh Chodesh celebrates the concept of perpetuity—notwithstanding life's peaks and plunges. And it is the woman who – through her steadfast faith – ensures our nation's survival; it is she who ensures that no matter how much we wane, we will always be renewed.