This is the 3113th most frequent Portuguese word.
boia
"Boia" means "float" or "buoy" in English.
In this sentence, ***boia*** is used in the context of a mechanical float (such as in a tank) that signals a specific state.
A boia do tanque indicou que estava cheio.
The tank's buoy indicated that it was full.
In this sentence, ***boia*** refers to a flotation device used to assist swimming or floating in water.
A boia ajudou o nadador a se manter flutuando.
The buoy helped the swimmer stay afloat.
Here, ***boia*** signifies a recreational or safety device brought to the beach for use in the water.