どだい土台dodai
1.

The structural element at the very bottom of a building that supports the entire structure, particularly in wooden constructions where it is a horizontal beam supporting the columns.

2.

The essential groundwork or underlying principle required for the development or progress of something, often referring to the fundamental aspects that must be established first.

3.

A term used to express the underlying premise or starting point of a situation, often indicating that a conclusion or outcome can be judged by returning to these fundamental aspects.

Example:

この家は土台がしっかりしている。