What is the X in X-mas?
also omphalus, "sacred stone," 1850, from Greek omphalos, literally "navel," later also "hub" (as the central point), from PIE *ombh-alo-, from root *nobh-/*ombh- "navel" (see navel). The name of the rounded stone in the shrine at Delphi, regarded by the ancients as the center of the world. Related: Omphalic.
omphalos om·pha·los (ŏm'fə-lŏs', -ləs)
n. pl. om·pha·li (-lī')