scarecrow

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

• noun A crude image or effigy of a person set up in a field to scare birds away from growing crops.
• noun Something frightening but not dangerous.
• noun A gaunt or haggard person.

from The Century Dictionary.

• noun The black tern, Hydrochelidon fissipes.
• noun A figure of straw or clouts, made in grotesque semblance of a man, set in a grain-field or a garden to frighten off crows and other birds from the crops; hence, anything set up or intended to frighten or keep off intruders, or to terrify the foolish.
• noun A person so poor and so meanly clad as to resemble a scarecrow.

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

• noun Anything set up to frighten crows or other birds from cornfields; hence, anything terifying without danger.
• noun A person clad in rags and tatters.
• noun (Zoöl.), Prov. Eng. The black tern.

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

• noun An effigy, typically made of straw and dressed in old clothes, fixed to a pole in a field to deter birds from eating seeds or crops planted there.
• noun figuratively, pejorative A tall, thin, awkward person.
• noun figuratively Anything that appears terrifying but offers no danger.
• noun A person clad in rags and tatters.
• noun UK, dialect A bird, the black tern.

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

• noun an effigy in the shape of a man to frighten birds away from seeds