n.

1. 预防；警惕；谨慎[U]
2. 预防措施[C][（+against）]
   I took an umbrella as a precaution.

   我带了一把伞以防下雨。

   We have taken necessary precautions against fire.

   我们已采取必要的防火措施。

n.

1. a measure taken in advance to prevent something undesirable happening.
2. (precautions) informal contraception.