challah

Let's take a look at the type of bread commonly eaten on shabbat, challah.

Philologos does a good job of explaining the background of the word here. To sum up the points of the article:

• The root of the word is חלל - which can mean either round or hollow
• Challah is part of the biblical commandment of hafrashat challah הפרשת חלה - separation of the challah

But there's more to it than that. Stahl brings up both the theory that challah comes from the roots meaning "round" (the shape of the loaf) or hollow (the form of the loaf). He adds another possibility - that the bread was sweet, and therefore received its name from the same root as the Arabic hilu (from which the sweet sesame paste halvah derives.)

Stahl also expands on the connection between the Shabbat bread challah and the obligation to separate challah. He quotes Rav Shmuel Gelbard in the Otzar Ta'amei Haminhagim, who explains that during the week, people would buy bread from the baker, who would perform the mitzva of seperating the challah. But before Shabbat, the women would bake the bread themselves, and in order to remind themselves to seperate challah - the bread itself began to be called challah.