Of or relating to the foundation or base; elementary: the fundamental laws of the universe. Forming or serving as an essential component of a system or structure; central: an example that was fundamental to the argument. Of great significance or entailing major change: a book that underwent fundamental revision. Physics Of or relating to the component of lowest frequency of a periodic wave or quantity. Physics Of or relating to the lowest possible frequency of a vibrating element or system. Music Having the root in the bass: a fundamental chord. Something that is an essential or necessary part of a system or object. Music The first harmonic in a harmonic series; the lowest harmonic. Physics The lowest frequency of a periodically varying quantity or of a vibrating system.