One way to hold this word: a sheet of paper with sand stuck to one side, and a hand moving it back and forth over wood. The high bits come off, the dust falls, and what is left is smooth. The two halves of the name say it all — sand for the rough grains, paper for the thing that carries them. Everything else the word does comes from that one picture: the sheet itself, and the rubbing.
From the word’s history
From sand plus paper: paper with sand on it. The grains on modern sandpaper are usually made in a factory rather than taken from a beach, but the name kept the original picture.
就是 sand（沙）加 paper（紙）組成的。早期真的是把沙黏在紙上，所以名字直接照著東西叫。今天上面多半換成人造的磨料，名字卻沒有跟著改——那個「沙黏在紙上」的畫面，就這樣留在字裡。
Wiktionary entry for sandpaper, etymology_text 'From sand + paper.' supplied in this packet (source_ref kaikki:3f6f69a190036ae4:1175158703:30840)
登入就可以看每一支怎麼連回核心畫面。