ὀμφᾰλό-εις · omphalo-eis — LSJ
having a navel, boss, with a central boss, with a knob on the top, pointing to the pole
having a navel or boss, ἀσπίδος -οέσσης of the shield with a central boss, Il. 6.118, Tyrt. 12.25, cf. Ar. Pax 1274 ; ζυγὸν-όεν yoke with a knob on the top, Il. 24.269, cf. ὀμφαλός II.2 ; οἰμωγὰς -οέσσας Ar. Pax 1278 (by comic transference from ἀσπίδας ὀ. ib. 1274) ; συκέης πόσιν -όεσσαν, prob. referring to a peculiar kind of fig (called ὀμφάλειος by Phot.), Nic. Al. 348 ; ἄρκτον -όεσσαν, because pointing to the pole (ὀμφαλός) of the heavens, ib. 7.