What is the term for a lower millstone used in food processing?

The term for a lower millstone used in food processing is indeed "meta." In ancient grain milling practices, two millstones were used: the upper millstone, which rotated, and the lower millstone, which remained stationary. The lower stone, or "meta," served as the base upon which the grain would be ground. This process was crucial for producing flour in ancient times, and the design of the millstones allowed for the efficient grinding of grain.

The other terms listed refer to different concepts or items within Roman culture but are not related to millstones. "Catillus" refers to a dish or shallow bowl used for serving food. "Ulus" does not pertain to milling but rather can be a suffix in Latin used to denote diminutive forms or related meanings. "Pecten" generally refers to a comb or ruffle, not linked to milling technology. Thus, "meta" is the correct and specific term associated with the function of the lower millstone in food processing.