The steel mesh and surrounding hardware at the end of a faucet. As water passes through the mesh, it mixes with air underneath the mesh. This is to reduce water flow while maintaining a good amount of force. Aerators are easily removed by unscrewing them.

A"ër*a`tor (&?;), n.

That which supplies with air; esp. an apparatus used for charging mineral waters with gas and in making soda water.

© Webster 1913

A"ër*a`tor (?), n.

That which supplies with air or gas; specif.:

(a)

An apparatus used for charging mineral waters with gas and in making soda water.

(b)

A fumigator used to bleach grain, destroying fungi and insects.

© Webster 1913