Tertian

In music theory, tertian (Latin: tertianus, "of or concerning thirds") describes any piece, chord, counterpoint etc.

[1] An interval such as that between the notes A and C encompasses 3 semitone intervals (A-B♭-B♮-C) and is termed a minor third while one such as that between C and E encompasses 4 semitones (C-D♭-D♮-E♭-E♮) and is called a major third.

A common triad chord can be regarded as consisting of a "stack" of two consecutive thirds.

The meantone temperament, a system of tuning that emphasizes pure thirds, may be called "tertian".

Tertian root movements have been used innovatively in chord progressions as an alternative to root motion in fifths, as for example in the "thirds cycle" used in John Coltrane's Coltrane changes, as influenced by Nicolas Slonimsky's Thesaurus of Scales and Melodic Patterns.

A progression of tertian chords in A minor (i-v-i-iv -i-v-I) ending on a Picardy third play ⓘ
Quartal chord on A equals thirteenth chord on B ♭ , distinguished by the arrangement of chord factors Play ⓘ . [ 3 ]