Englishfor English speakers
certainty
Noun
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Certainty is the state of being 100% sure.
It's a little too early to say that with absolute certainty.
The doctor could not say what was wrong with any degree of certainty.
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If something is a certainty, it is sure to happen.
The expected change became a certainty two weeks ago.
We need to accept the certainties of aging, illness, and death.
index
Noun
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An index is an alphabetical (A to Z) list, usually at the back of a book, where you can find the pages in a book that talk about particular things or words.
Look in the index to see where they talk about Chomsky.
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An index shows the level of prices, wages, etc. so you can compare them with those of an earlier date.
On Wall Street, the Dow Jones index closed 10 points up at 2,731.23.
index
Verb
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If you index something, you make an index (guide) for it.
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If you index something to a certain price level, you make it go up or down with that level.