Sixth chords
A sixth chord is a 4-note chord — the root plus a major third, a perfect fifth and a major sixth above it. It is a major triad with a major sixth added above the fifth.
It sounds sweet and vintage, popular in jazz, swing and older pop. Below are the sixth chords for all twelve keys, from C to B — pick any chart for its full set of voicings, the piano shape and how it's built.