Taharah and tumah, both very important terms for Jewish ritual law as laid out in the Torah, are usually translated as 'purity' and 'impurity', or something similar. As has often been noted, it's not clear that these are actually good translations for these terms. In practice the terms tend to mean 'ability to be immersed in the life of the community as called by God' and 'inability to be immersed in the life of the community as called by God', and the standard rabbinical interpretations (taking their cue from verses like Psalm 19:9, "The fear of the Lord is tehorah, enduring forever") see a link between taharah and what endures. The laws governing taharah are the laws governing one's fitness for representing the enduring the covenant God has made with Israel. Thus, tumah is almost always associated with death or physical loss.
And this seems to be about right. The Biblical book that is most insistent on issues of taharah and tumah, Leviticus, is the one that is most insistent on the Election of Israel: "I, the Lord, am your God" is its repeated refrain: Be holy, for I, the Lord, am holy, and I, the Lord, make you holy (cf. 20:7-8). And in Numbers (35:34) the children of Israel are told "Do not tameh the land in which you will live, in which I dwell, for I the Lord dwell among the children of Israel." Interestingly as well, the Bible looks with appoval on a certain kind of tumah, when the kings of Israel render unfit for use the places and instruments of idolatry (2 Kings 23; cf. Isaiah 30:19-22).
Similarly, one of the passages in the Bible which talks most about taharah, is the description of the Tabernacle in Exodus, in which the purity is simply the purity of gold without dross (cf. the important usage in Psalm 12:6). This suggests, actually, a great number of possible translations, since there are many words for purity in the sense used of metals, depending on the process and on what is in view: parted, cupellated, tried, assayed, refined, etc. Taharah would then apply when something has been refined, parted from the dross of the unenduring to leave only the enduring; tumah would apply when a thing becomes associated with the unenduring, needing to be tried and assayed again in order to symbolize the dwelling of the Lord with Israel through His enduring love.
UPDATE: Ed Cook of Ralph the Sacred River informs me that the transliteration here should be tohorah rather than taharah.