It's a symmetric relationship. If a note looks like a chord then a chord looks like a note. Both a mix of frequencies and a single frequency can produce the same colour, so they both look like each other.
Basically any note played on an analog instrument has a set of overtones of various frequencies. If these tones were played a bit louder, you would hear a chord rather than a single note.
When?
[severely edited, trying to fix bad writing]