Definition of fundamental

• the lowest tone of a harmonic series
• being or involving basic facts or principles; "the fundamental laws of the universe"; "a fundamental incomatibility between them"; "these rudimentary truths"; "underlying principles"
• far-reaching and thoroughgoing in effect especially on the nature of something; "the fundamental revolution in human values that has occurred"; "the book underwent fundamental changes"; "committed the fundamental error of confusing spending with extravagance"; "profound social changes"