quitter

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One who gives up easily.

from The Century Dictionary.

• To suppurate.
• noun One who quits.
• noun A deliverer.
• noun Matter flowing from a sore or wound.
• noun In farriery, a fistulous wound upon the quarters or the heel of the coronet, caused by treads, pricks in shoeing, corns, or other injuries which produce suppuration at the coronet or within the foot.
• noun Scoria of tin.
• noun One who quits or gives up in the face of difficulties; one who has not the courage or determination to finish what he undertakes to do.
• noun Specifically, a workman who has the habit of throwing up his job on slight pretenses.
• noun A young male fur-seal, old enough to enter the breeding grounds toward the close of the season, but not strong enough and bold enough to hold his ground when disturbed: he therefore quits his place.

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

• noun One who quits.
• noun obsolete A deliverer.

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

• noun Jamaica Matter flowing from a wound or sore; pus.
• noun A fistulous wound at the top of a horse's foot resulting from bruises, pricks, or neglected corns.
• noun obsolete Scoria of tin.
• verb To suppurate; ooze with pus.
• noun One who quits.
• noun obsolete A deliverer.

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

• noun a person who gives up too easily