1. An unstable or inadequate structural foundation; a weak base upon which something is built
The building has a weak foundation and will need major repairs.
O edifício tem um alicerce fraco e precisará de grandes reparos.
2. Figuratively: an unstable or insufficient basis for an argument, relationship, or endeavor
Their relationship was built on a weak foundation of lies.
O relacionamento deles foi construído sobre um alicerce fraco de mentiras.