A scar where the umbilical cord was attached(noun)
WordNet. Princeton University. 2010.
Use "omphalus" in a sentence
"Jupiter Ammon was esteemed of the highest antiquity, and we are informed that there was an omphalus here; and that the Deity was worshipped under the form of a navel."
"It is observable, that this historian does not mention an omphalus: but says, that it was a statue, ξοανον, which was carried about."
"Pausanias gives this account of the omphalus at Delphi."