fun·da·men·tal 
(fŭn′də-mĕntl)
(fŭn′də-mĕntl)adj.
1.
a. Of or relating to the foundation or base; elementary: the fundamental laws of the universe.
b. Forming or serving as an essential component of a system or structure; central: an example that was fundamental to the argument.
c. Of great significance or entailing major change: a book that underwent fundamental revision.
2. Of or relating to the lowest possible frequency or the lowest frequency component of a vibrating element, system, periodic wave, or quantity: a fundamental chord.
3. Music Having the root in the bass: a fundamental chord.
n.
1. Something that is an essential or necessary part of a system or object.
2. The lowest frequency of a periodically varying quantity or of a vibrating system.
fun′da·mental·ly adv.