People or things that spew, or send out, a lot of something, like liquid or gas.
Spewers can be machines, volcanoes, or even people who are sick.
Examples:
The volcano is one of the biggest spewers of lava in the world.
The factory's smokestacks are spewers of pollution.
The sick person is a spewer of germs.
The baby is a spewer of food when he doesn't like it.
The fire hydrant is a spewer of water when it's broken.
The dragon is a spewer of fire in the story.