RITUAL IMPURITY, specifically menstrual (Leviticus 15:19-24, now on these pages) — and by extension anything that must be kept at a distance. ⚠ The word's plainest legal use is at Leviticus 12 (already on these pages), which twice defines a new mother's first days by comparison to it — unclean 'as in the days of her niddah' — without ever explaining the comparison, because the law it points at (Leviticus 15) is assumed known. Read there rather than in the prophets, it is what tame always is: a temporary bar on approaching the sanctuary, not a fault and not a verdict. ⚠ Lamentations then plays on it: verse 8 says Jerusalem became a nidah (from a root meaning to shake the head, so 'an object of head-shaking') and verse 17 says she became a niddah among the nations. The two words are near-identical and the poem almost certainly means both at once. The versions split badly there — KJV 'removed' at v8 and 'a menstruous woman' at v17; ASV 'an unclean thing'; NWT 'an object of disgust' — which is why this translation renders each verse as it stands and notes the play. The distance between that metaphor and the purity rule is exactly the distance this dictionary exists to show. ⚠ Numbers 19 makes the word do something startling: the purification water itself is called me niddah, 'water of NIDDAH' — the stuff that removes impurity named after impurity. The shelf scatters (KJV 'water of separation', ASV 'water for impurity', NIV and NWT 'water of/for cleansing', Geneva 'sprinkling water'), and the two Reina-Valeras take opposite sides, RV60 «agua de purificación» against RV 1909 «agua de separación». The Douay-Rheims renders the same two words three different ways inside that one chapter. → first discussed at Lamentations 1:8