What does "accompaniment" mean?

Accompaniment: That which accompanies; something that attends as a circumstance, or which is added to give greater completeness to the principal thing, or by way of ornament, or for the sake of symmetry. Specifically: (Mus.) A part performed by instruments, accompanying another part or parts performed by voices; the subordinate part, or parts, accompanying the voice or a principal instrument; also, the harmony of a figured bass. P. Cyc.