Definitions of fundamental:

• noun:   the lowest tone of a harmonic series
• adjective:   being or involving basic facts or principles

  Example: "The fundamental laws of the universe"

• adjective:   far-reaching and thoroughgoing in effect especially on the nature of something

  Example: "The fundamental revolution in human values that has occurred"

• adjective:   serving as an essential component

  Example: "An example that was fundamental to the argument"