A condenser can be pictured as the place in a machine where something loose and spread out is gathered and packed into a smaller, denser form: hot gas pulled back into drops of liquid, electricity held in one small store, scattered light brought onto a single bright spot. The word always names a part, never the whole machine.
From condense + -er, literally the thing that condenses.
從 condense（凝聚、變濃）加 -er（做這件事的東西）來的，字面就是「做凝聚這件事的裝置」。這條線索跟上面的畫面是同一件事：所有用法都圍著「收攏」打轉。
Wiktionary entry for condenser, etymology supplied in this packet (kaikki:3f6f69a190036ae4:1381451787)
Two branches
把氣體收回成液體
這是最字面的一支：被收攏的就是物質本身。氣體散開、體積大，帶走熱之後聚回液體、體積小，收攏的動作用眼睛就看得到。
noun · B2
A piece of equipment that cools a gas until it turns back into a liquid. A condenser is normally one part inside a bigger machine, such as a steam engine, a fridge, an air conditioner, or a laboratory still.
冷凝器
把散開的東西聚到一處
同樣是收攏，但收的不是物質。光和電都會散掉、留不住，這一支的零件負責把它們集中到一個小地方。畫面一樣，被收的東西換了。
noun · C1
A lens, or a set of lenses, that gathers light and aims it at one small spot — for example the part under a microscope stage that lights up the slide you are looking at.
聚光鏡