Niddah names the season of separation that follows a woman's flow of blood (Leviticus 15:19), and the lexicons root it in the family of nadad, to be distant, to move away. Hear the design in that: the word describes distance, not disgrace. It is a status with an appointed end, and the end runs through water.

English has treated it badly. The KJV says "put apart" and "separation," the NIV says "monthly period," and Ezekiel's searing image gets medicalized into "monthly uncleanness." Flattened that way, the word sounds like plumbing or like shame, and it is neither. It is the Torah's name for the kind of impurity you cannot scrub off yourself.

Which is exactly why the prophets promote it. When Yechezkel needs to name what Israel's way had become before HaShem, he says it was "like the tumah of the niddah" (Ezekiel 36:17), and the same chapter answers with clean water and a new heart. When Zecharyah opens the last-days fountain, it is "for sin and for niddah" (Zechariah 13:1). The deepest distance is the one the fountain is opened for. The word carries its own homecoming.