Base
A four letter word meaning the foundation of something is base.
The word you are looking for is "foundation." A foundation is a base or support structure upon which something else rests or is built.
The foundation of something can be described as its "base." The base of an object or concept is its fundamental support or underlying structure. It provides stability and strength to the rest of the entity.
If you take off CH from the word chase (the first two letters) and add a letter (B) you end up with the word base. A base is the support or foundation of something.
The root word of foundation is "found," which comes from the Latin word "fundare" meaning "to lay the bottom of something."
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base
The English-Latin translation for the word foundation is fundamentum. Foundation mean the underlying basis or principle for something or the lowest load-bearing part of a building.
To undermine means to weaken or subvert something, such as an authority, reputation, or system, often through indirect or insidious means. It can also refer to eroding the foundation or support of something.
The word base means the same as foundation, bottom, or support.
Adundance is not a word. Abundance, which you may mean, is a word. It means there is a lot of something. It means there is plenty of something.
The Greek word "monos" is the foundation for the modern English word "monochrome," which refers to something in a single color or shades of a single color.