Notes sounded as one — agreement made audible. Strings pressed together into a single name.
The musical chord is a 16th-century clipping of accord (Latin accordare, ad- + cor, heart — 'hearts together'), later respelled with an 'h' by confusion with the unrelated chorda (Greek khorde, a gut string), the word behind mathematical and anatomical 'chord.'
A chord is not several sounds merely occurring together but several recognized as consenting to sound together, which is closer to a verdict than a coincidence — change one note and the agreement is void, whatever the ear still hears as pleasant.