What is a synonym for "substruction"?

Common synonyms include: base, basement, basis, bed, bedding, bedrock.

Substruction

noun

noun ·Rare ·Advanced level

Noun

1
underbuilding; substructure
"It is a magnificent strong building, with a substruction very remarkable."
2
foundation; base figuratively

"It is a magnificent strong building, with a substruction very remarkable."

From Latin substructio, from substruere, substructum (“to build beneath”), from sub (“under”) + struere (“to build”).