1. 伞；雨伞；阳伞
    An umbrella is an object which you use to protect yourself from the rain or hot sun. It consists of a long stick with a folding frame covered in cloth.

umbrella

    e.g. Harry held an umbrella over Dawn.
           哈里为唐打着伞。

2. 综合团体；总称；统称
    Umbrella is used to refer to a single group or description that includes a lot of different organizations or ideas.

umbrella是什么意思

    e.g. Does coincidence come under the umbrella of the paranormal?...
           巧合属于超自然现象吗？
    e.g. Within the umbrella term 'dementia' there are many different kinds of disease.
           “痴呆”这一统称里包括多种不同的疾病。

3. 保护伞（指保护某个国家或群体的体制或协议）
    Umbrella is used to refer to a system or agreement which protects a country or group of people.

    e.g. The major powers have chosen to act under the moral umbrella of the United Nations...
           世界主要大国都选择在联合国的道义框架下行事。
    e.g. Britain cannot avoid being under the US nuclear umbrella, whether it wants to or not.
           不管愿不愿意，英国都免不了要处于美国的核保护伞之下。