French sixth chord

A French sixth chord is a tetrad comprising a root, major third, augmented fourth, and augmented sixth.

English Wikipedia has an article on:

Augmented sixth chord #French sixth

In just intonation

In the 5-limit:

• 128:160:180:225 is found rooted at ♭II (16⁄15) and ♭VI (8⁄5) in the duodene.