The Mishna, as I'm sure you all recall, says that the KG would sprinkle the sacrificial blood on the Mizbeach HaPnimi's טוהר. One explanation of the word is that it means "noon," ie, middle, as in Aramaic טהרייא from Hebrew צהריים. The other explanation is that it means גילוי, ie, top, as in the phrase עצם השמים לטוהר.
1) How does טוהר in the passuk mean גילוי? If anything, it should mean purity. (Maybe it's a לשון of clarity?)
2) If we roll the two explanations together to say that טוהר and צוהר are one and the same and they mean גילוי, then the phrase צוהר תעשה לתיבה would make sense as refering to a window, as is in fact one shitta in Rashi.
3) If we accept 2 (which we may possibly not want to do), then it is interesting that the word זוהר and בוהר both mean light. (At the end of the day, the word light is used as an expression of גילוי, as in the passuk אִם-בַּמַּחְתֶּרֶת יִמָּצֵא הַגַּנָּב, וְהֻכָּה וָמֵת--אֵין לוֹ, דָּמִים. אִם-זָרְחָה הַשֶּׁמֶשׁ עָלָיו, דָּמִים לוֹ: שַׁלֵּם יְשַׁלֵּם--אִם-אֵין לוֹ, וְנִמְכַּר בִּגְנֵבָתוֹ.

ETA: Then, accepting Gabbe's theory of Shoresh heirarchy, the words בוהר, זוהר, טוהר, and צוהר all would share the shoresh אור. (The aleph/heh switch wouldn't be much of a problem because the shoresh of להורות is אור too, IIRC)

why not the shoresh הרר ?