Someone or something who barks.

"My neighbor's dog is a constant barker that keeps me awake at night."

A person employed to solicit customers by calling out to passersby, e.g. at a carnival.

"Bob had amassed a considerable stockpile of double entendres from his days working as a barker for a strip joint."

A shelf-talker.

A video game mode where the action is demonstrated to entice someone to play the game.

"The barker mode of the arcade video game convinced the teenager to spend a quarter."

A pistol.

The spotted redshank.

A person who removes needed or valuable tree bark, as on a cinnamon or cinchona plantation.

"The professor of barker has been made largely obsolete by the realization that in most cases saplings can be cultivated far more profitably."

A tanner.

"The profession of barker has been made largely obsolete by the introduction of more effective tanning agents, but it lives on as a surname."

A machine used to remove unneeded bark from wood.

"Run these logs through the barker so we can use them as fence posts."