一把雨伞在英语中可以称为 "an umbrella"。这个词源自拉丁文 "umbra"，意思是影子。雨伞最初可能是用来挡住阳光，以避免人们被晒伤，但后来被用来防护雨水。

例句：

Don't forget to take an umbrella with you. It looks like it might rain.（不要忘记带上一把雨伞。看起来可能会下雨。）

She opened her umbrella and held it over her head to keep the rain off.（她打开了她的雨伞，把它架在头上以防止雨水。）