BT Tan 22b(26)var. :כי כסיא/כיסא/ דתנורא או דלמא כידרא דהדר אפומא דתנורא‏ : is it like the covering of an oven or perhaps like the row (of baked stuff) that surrounds the opening of the oven †
See the entire entry for kysˀ#2 n.m. covering(??)

BT Tan 22b(26) :כסיא דתנורא‏ : the cover of the oven
See the entire entry for ksāy, ksāyā v.n. covering