robber

from The Century Dictionary.

• noun One who robs; one who commits a robbery; in a looser sense, one who takes that to which he has no right; one who steals, plunders, or strips by violence and wrong.
• noun Synonyms Robber, Thief, Pilferer, Freebooter, Marauder, Brigand, Bandit, Pirate, depredator, despoiler, rifler, highwayman, footpad. (See pillage, n.) A thief takes other people's property without their knowledge; a robber takes it openly, whether or not resistance is offered: in a looser sense, thief is often applied to one who takes a small amount, and robber to one who takes a large amount. A pilferer takes very small amounts by stealth. A freebooter and a marauder rove about, robbing and plundering: the word freebooter emphasizes the fact that the man helps himself at his pleasure, while marauder suggests the loss, inconvenience, fright, or distress produced. A brigand or bandit is one of an organized band of outlaws and robbers, especially in certain countries long known as infested with such bands; bandit is rather a poetic or elevated word; brigand is more common in prose. A pirate is a brigand of the sea. All these words have considerable extension by metonymy or hyperbole.
• noun In bee-keeping, a boo which takes honey from a strange hive.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who robs; in law, one who feloniously takes goods or money from the person of another by violence or by putting him in fear.
• noun (Zoöl.) Any hermit crab.
• noun (Zoöl.) Same as Hornet fly, under Hornet.
• noun (Zoöl.) a jager gull.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A person who robs.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a thief who steals from someone by threatening violence