根底

1. Origins, structure, and basic meaning

• Structure: 根底 (こんてい) is an abstract noun for the deepest underlying basis of an opinion or relationship.
• Basic usage: 意見の根底には願いがある locates a shared motive beneath two opinions, while 関係の根底が崩れる makes the underlying basis collapse when trust is shaken.

2. Common pitfalls and similar expressions

• Underlying basis rather than a physical bottom
  • Both 意見の根底 and 協力関係の根底 concern a hidden basis of thought or relationship. Even with 崩れる, the example is not about the physical bottom of a structure.