IPA: //ˈlaɪfˌbɔɪ//
KK: /ˈlaɪfˌbɔɪ/
A buoy designed to be thrown to a person in water to provide flotation and help them stay afloat until rescue.
The lifeguard threw a lifebuoy to the swimmer who was struggling in the water.
Lifebuoy → It is formed from "life" (from Old English "līf", meaning existence or living) and "buoy" (from Middle English "boie", meaning to float or support). The word "lifebuoy" refers to a floating device that supports or saves a person in danger of drowning, thus preserving life.
Think of a device that helps keep someone 'alive' ('life') by 'floating' ('buoy') in water — that's why a lifebuoy is a life-saving float.
No commonly confused words.