adjective / noun
fundamental
fun-duh-MEN-tul/ˌfʌndəˈmentl/
An essential basis of something, or forming that basis.
A solid foundation is fundamental to the strength of the wall.

Etymology
Something fundamental belongs to the foundation on which other things depend. That supporting-base image extends to essential principles or features underlying a subject or system.
In context
logic is the most fundamental aspect of our intelligence if you don't have a firm sense of logic you will be all over the place but logic is the foundation
More examples
- The course teaches the fundamentals of drawing.
- Trust is fundamental to their partnership.
- He overlooked a fundamental problem in the design.
Forms
fundamental · fundamentals
fundamentally adverb — At the most basic level.
Similar words
- essential
- Emphasizes necessity rather than a foundational role.
- foundational
- Foundational emphasizes supporting other ideas or structures.