fundamental

noun1 of 2

relating to the most important parts of something

• “There is a fundamental difference between your opinion and mine.”Tatoeba
• “This is a fundamental question that needs to be addressed.”Tatoeba

Sentences from Tatoeba show real usage. A word can have several meanings, so a sentence may use another one.

adjective2 of 2

Pertaining to the foundation or basis; serving for the foundation.