vampire

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

• noun In popular folklore, an undead being in human form that survives by sucking the blood of living people, especially at night.
• noun A person, such as an extortionist, who takes advantage of others, especially for personal gain.
• noun A vampire bat.

from The Century Dictionary.

• noun A kind of spectral being or ghost still possessing a human body, which, according to a superstition existing among the Slavic and other races on the lower Danube, leaves the grave during the night, and maintains a semblance of life by sucking the warm blood of living men and women while they are asleep.
• noun Hence, a person who preys on others; an extortioner or blood-sucker.
• noun Same as vampire-bat.
• noun Theat., a small trap made of two flaps held together by a spring, used for sudden appearances and disappearances of one person.
• Of or pertaining to a vampire; resembling a vampire in character; blood-sucking; extortionate; vampiric.

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

• noun A blood-sucking ghost; a soul of a dead person superstitiously believed to come from the grave and wander about by night sucking the blood of persons asleep, thus causing their death. This superstition was once prevalent in parts of Eastern Europe, and was especially current in Hungary about the year 1730. The vampire was often said to have the ability to transform itself into the form of a bat, as presented in the novel depicting the legend of Dracula published by Bram Stoker in 1897, which has inspired several movies.
• noun Fig.: One who lives by preying on others; an extortioner; a bloodsucker.
• noun (Zoöl.) Either one of two or more species of South American blood-sucking bats belonging to the genera Desmodus and Diphylla; also called vampire bat. These bats are destitute of molar teeth, but have strong, sharp cutting incisors with which they make punctured wounds from which they suck the blood of horses, cattle, and other animals, as well as man, chiefly during sleep. They have a cæcal appendage to the stomach, in which the blood with which they gorge themselves is stored.
• noun (Zoöl.) Any one of several species of harmless tropical American bats of the genus Vampyrus, especially Vampyrus spectrum. These bats feed upon insects and fruit, but were formerly erroneously supposed to suck the blood of man and animals. Called also false vampire.
• noun (Zoöl.) a vampire, 3.

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

• noun colloquial A person with the medical condition Systemic lupus erythematosus, colloquially known as vampirism, with effects such as photosensitivity, brownish-red stained teeth, and increased night vision.

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

• noun (folklore) a corpse that rises at night to drink the blood of the living