Hold the object first: a cone, wide at one end, that you speak into so your voice goes one way and goes far. A small sound leaves it as a large one, and everyone in front of it hears the same words at the same time. Every other use keeps that shape. A magazine that carries a small group's message is the cone. A government that makes its demands in public instead of in a meeting room is talking through the cone at another country. The word never means that the message is better — only that it has been made louder and pointed somewhere.
From the word’s history
The source gives the word as mega- (big) plus -phone (sound), which lines up exactly with what the object does.
來源資料說這個字是 mega-（大）加 -phone（聲音）。這正好對上那個器具在做的事：把聲音變大。
Wiktionary entry for megaphone (etymology 1), etymology_text supplied in this packet: "From mega- + -phone." (source_ref kaikki:3f6f69a190036ae4:1180096939)
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