means A device that converts electrical signals into sound, or a person who speaks aloud — especially one addressing an audience or presiding over an assembly.

from From the verb "speak," which traces back to Old English "specan" (an alteration of earlier "sprecan"), with cousins in Old High German "sprehhan" and the modern German "sprechen." The "-er" simply marks the doer: one who speaks. The human sense came first by centuries; the audio-device sense is a much later borrowing, naturally extended once machines began doing the talking for us.