hypobasis

[ hahy-poh-bey-sis ]
/ ˌhaɪ poʊˈbeɪ sɪs /

noun, plural hy·po·ba·ses [hahy-poh-bey-seez] /ˌhaɪ poʊˈbeɪ siz/. Architecture.

the lowermost distinctively treated part of a base.
a lower base beneath an upper and more important one.

Origin of hypobasis