Chords that consist of two notes of an interval of a fifth, without the note that determines whether they are major or minor,and when they are played on the guitar,in more than two notes are referred to by the majority of folk musicians as modal chords.
rock musicians tend to use the term power chords, with reference to two note fifth chords.
The dictionary definition of a chord is the simultaneous and harmonious union of sounds of a different pitch.
therefore a chord can be TWO NOTES as well as three notes or as many notes as you want, provided they are a simultaneous and harmonious union of sounds, so two notes can be described as you did correctly as an interval when they are played one after another or together and they can also be described correctly as a chord when played together.
go to any guitar workshop and musicians refer to modal chords, in the same way as they refer to major or minor chords,modal chords do exist and they consit of any two notes or more, that do not have a major or minor thirds, and have interval of fifths.
They can of course have added notes the same as major or minor chords can. C MODAL 9 would be cgcgcd, cmajor 9 would be cegd, c minor 9 is c eflat g d.
Modal chords exist and the world is not flat.