lifebelt

noun

1. 救生圈
   a large ring made of material that floats well, that is used to rescue sb who has fallen into water, to prevent them from drowning
2. （使人不下沉的）救生带
   a special belt worn to help sb float in water

1. 救生圈
   A lifebelt is a large ring, usually made of a light substance such as cork, which someone who has fallen into deep water can use to float.