tertsiaal
Tertsiaal is a term used in various contexts, most notably in music and geology. In music theory, a tertsiaal refers to an interval spanning three diatonic scale degrees, such as a third. This could be a major third, minor third, or augmented third. The concept of thirds is fundamental to understanding harmony and chord construction in Western music. For example, a triad is typically built by stacking two thirds on top of each other.
In geology, the term tertsiaal describes a specific geological period, also known as the Tertiary Period. This