One way to hold it: quick with -ie stuck on the end, the way English makes a short, friendly noun. What you get is the quick one. Sometimes the quick one is a thing that takes almost no time; sometimes it is the person who does something faster than anybody else.
可以想成 quick 後面加了 -ie，英文很習慣這樣把一個字變得又短又親切，做出一個口語名詞：「快的那一個」。有時候那個「快的」是一件幾乎不佔時間的事，有時候是動作比誰都快的那個人。
From the word’s history
The source gives the formation directly: quick plus the suffix -ie.
來源直接說明了造字方式：quick 加上字尾 -ie。
Wiktionary, "quickie"
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