People worried about tooth decay, cavities, or caries, might consider themselves in a precarious position. That is to say, they might envision their circumstances as uncertain, and their situation insecure. (来源：英语学习门户 http://www.EnglishCN.com)

However, we are here to assure anyone anxious about their teeth that there is no etymological link between the words precarious and caries. Caries comes from the Latin word for "decay" which has kin in a Greek word for "death," a Sanskrit word for "he breaks," and an Old Irish word meaning "it decays."

People praying their teeth don't decay are a lot closer to the word precarious than they might suspect. Precarious, which first appeared in print in 1646, a dozen years after caries, shares a Latin ancestor with the word prayer. Both precarious and prayer count among their linguistic kin the Latin precarius (spelled without an "O"), meaning "obtained by entreaty."

What was so precarious about the long ago precary (a now-obsolete noun precursor of the adjective precarious)? It named a grant made on request but revocable whenever the grantor pleased. One early, now-archaic sense of precarious was "depending on the will or pleasure of another; held on sufferance."

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