Major, minor, augmented and diminished chords are all triads - three note chords. Another useful type of triad is the suspended chord. In suspended chords, the 3rd is replaced by the 4th degree of the scale it is derived from. Because these chords have no 3rd degree, they work equally well in both major and minor keys.
Suspended chords often resolve back to a major or minor chord of the same letter name as demonstrated below.