tzohar

In this weeks parasha (Bereshit 6:16), Noach is commanded to "make a tzohar in the ark" צֹהַר תַּעֲשֶׂה לַתֵּבָה

The word tzohar (or tsohar) appears only here in the Tanach and there are a number of explanations for the meaning:

• window (Onkelos, Rashi, Ibn Ezra) - based on tsohorayim צהרים - noon. The light of noon is compared to the light entering the ark via the window. Also related to zohar זוהר - brilliance. This may be the window mentioned in 8:6.
  
• lamp, or oil for a lamp (Menachem, Radak, Chizkuni)- based on yitzhar יצהר - oil.
  
• roof (Shadal, Cassuto, Kaddari) - via Arabic zahr, Akkadian seru, Ugaritic zr - meaning "back, top".
  
• luminous stone (Rashi) - based on a Midrash

Klein connects the first three interpretations. He offers a root צהר , meaning "to be bright, clear". He translates yitzhar as "fresh oil" and says it means either "that which newly appears" or "that which shines". He also writes that the Arabic zahara means "appeared, became visible", and this is connected to the roots meaning "back, top". Therefore tzohorayim means "culminating point, zenith". Stahl explains it somewhat differently, by saying that at noon, the sun begins turning away from us.

Based on the root צהר Ben Yehuda coined הצהיר - to declare, from the sense of putting something for all to see, in the light of day (the Biblical verb הצהיר - Iyov 24:11 - meant "to make yitzhar".) Apparently the coinage of Ben Yehuda (who died in 1922) caught on quickly, for the Balfour declaration (in 1917) is known as הצהרת בלפור - Hatzharat Balfour, and not הכרזת בלפור - Hachrazat Balfour which would have used the older verb הכריז.