看身體裡面：少，但不能沒有
把那一點點的量放進生物體裡，並且加上一個條件：這一點點是必需的。
noun · B2
A chemical element that a living body needs in a very small amount in order to work properly. The amount is tiny, but without it the body cannot do certain jobs.
微量元素
核心畫面
Hold the word trace first: what is left when there is almost nothing left - a mark you can just about find. Now put that amount of a chemical element somewhere. Each meaning on this page only changes where you are looking: inside a body, inside a sample, or across the whole planet.
先抓住 trace 這個字：幾乎什麼都不剩的時候，剩下的那一點點痕跡。找得到，但少到幾乎不見。現在把這麼一點點的化學…更多收起
先抓住 trace 這個字：幾乎什麼都不剩的時候，剩下的那一點點痕跡。找得到，但少到幾乎不見。現在把這麼一點點的化學元素放進某個地方。這一頁三個意思的差別，只在於你往哪裡看。看身體裡面，看手上那份樣品裡面，還是看整顆地球。量都是「少到只剩痕跡」，變的是範圍。From the word’s history
The supplied source calls this a compound of trace, a very small amount, plus element, a chemical element. The word says its own meaning: the element that is only there in traces.
來源資料說這是 trace（極少的量）加 element（化學元素）組成的複合詞。所以這個詞把自己的意思寫在臉上：只以痕跡般的量存在的元素。
Wiktionary entry supplied in this packet (source_ref kaikki:3f6f69a190036ae4:1436237806): Compound of trace (very small amount) + element (chemical element).
Two branches
看量有多少：在樣品裡，還是在地球上
這一族不談需不需要，只談量。差別在於量是在哪個範圍裡數的。
noun · C1
In chemistry, a chemical element that is present in whatever is being tested - a rock, some soil, water, a metal - in only a very small amount.
微量元素（樣品中）