A clear, light, easily burned plastic that could be drawn out into a long strip — the strip that moving pictures were printed on. Hold that strip and the rest follows: first the material itself, then the whole of cinema, named after the stuff it used to be carried on.
可以想成一條透明、又輕、又怕火的塑膠長帶——電影畫面一格一格就印在上面。抓住這條帶子，其他意思就順著出來：先是這種材料本身，然後整個電影世界乾脆就用「載著電影的那個東西」來稱呼。
From the word’s history
The name was a company trademark: cellulose plus -oid, 'the stuff like cellulose'. The name says what it is made of, which is why it stayed attached to the strip, and then to the films the strip carried.
這個名字本來是一家公司的商標：cellulose（纖維素）加上 -oid（像…的東西），字面就是「像纖維素做出來的那種材料」。名字直接說出它的成分，所以它牢牢黏在那條膠卷上，後來也跟著黏到膠卷承載的電影上。
Wiktionary, "celluloid"
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