ghost

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

• noun The spirit of a dead person, especially one that is believed to appear to the living in bodily form or to haunt specific locations.
• noun A person's spirit or soul.
• noun A returning or haunting memory or image.
• noun A slight or faint trace.
• noun The tiniest bit.
• noun A faint, unwanted image, as.
• noun An unwanted image on a television or radar screen caused by reflected waves.
• noun A displaced image in a photograph caused by the optical system of the camera.
• noun An unwanted spectral line caused by imperfections in a diffraction grating.
• noun A displaced image in a mirror caused by reflection from the front of the glass.
• noun Informal A ghostwriter.
• noun A nonexistent publication listed in bibliographies.
• noun A fictitious employee or business.
• noun Physiology A red blood cell having no hemoglobin.
• intransitive verb Informal To engage in ghostwriting.
• intransitive verb To move noiselessly like a ghost.
• intransitive verb To haunt.
• intransitive verb Informal To ghostwrite.

from The Century Dictionary.

• To appear to in the form of a ghost; haunt as a spirit or specter.
• To give up the ghost; die; expire.
• noun One who does literary, legal, or artistic work for another, who gets all the credit; one who ‘devils’ for another.
• noun A false line in a diffraction-spectrum caused by certain periodic irregularities in the ruling of the grating which produces the spectrum. Ghosts usually occur in pairs accompanying a conspicuous line on each side of it and near it. See grating.
• noun A red blood-corpuscle from which the red coloring-matter or hemoglobin has escaped.
• noun Breath; spirit; specifically, the breath; the spirit; the soul of man.
• noun The soul of a dead person; the soul or spirit separate from the body; more especially, a disembodied spirit imagined as wandering among or haunting living persons; a human specter or apparition.
• noun A spirit; a demon.
• noun A spirit in general; an unearthly specter or apparition.
• noun A dead body.
• noun A mere shadow or semblance.
• noun In optics, a spot of light or secondary image caused by a defect of the instrument, generally by reflections from the lenses.
• noun Specifically In photography, a glint of light cast by the lens on the focusing-glass or on the plate during exposure, in the latter case producing a more or less defined opaque spot. It results usually from the presence of a too strongly illuminated surface or object in or near the field of the lens. Also called flare.
• noun An order founded at Montpellier, France, about the end of the twelfth century, and united to the Order of St. Lazarus by Pope Clement XIII.
• noun A Neapolitan order. See Order of the Knot, under knot
• noun Synonyms Ghost, Shade, Apparition, Specter, Phantom, Phantasm. Ghost is the old word for the disembodied spirit, especially as appearing to man: as, the ghost of Hamlet's father; the ghost of Banquo. Shade is a soft and poetic word for ghost: as, the shade of Creüsa appeared to Æneas. An apparition is a ghost as appearing to sight, perhaps suddenly or unexpectedly; it may also be a fancied appearance, while a ghost is supposed to be real: as, Jupiter made a cloud into an apparition of Juno; Macbeth saw an apparition of a dagger; the witches showed him an apparition of a crowned child. A specter is an alarming or horrifying preternatural personal appearance, having less individuality, perhaps, than a ghost or shade, but more than an apparition necessarily has. A phantom has an apparent, not a real, existence; it differs from a phantasm in emphasizing the unreality simply and in representing a single object, while phantasm emphasizes the deception put upon the mind, and may include more than one object.

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

• intransitive verb obsolete To die; to expire.
• transitive verb obsolete To appear to or haunt in the form of an apparition.
• noun obsolete The spirit; the soul of man.
• noun The disembodied soul; the soul or spirit of a deceased person; a spirit appearing after death; an apparition; a specter.
• noun Any faint shadowy semblance; an unsubstantial image; a phantom; a glimmering
• noun A false image formed in a telescope by reflection from the surfaces of one or more lenses.
• noun (Zoöl.) a large European moth (Hepialus humuli); so called from the white color of the male, and the peculiar hovering flight; -- called also great swift.
• noun the Holy Spirit; the Paraclete; the Comforter; (Theol.) the third person in the Trinity.
• noun to die; to expire.

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

• noun rare The spirit; the soul of man.
• noun The disembodied soul; the soul or spirit of a deceased person; a spirit appearing after death; an apparition; a specter.
• noun Any faint shadowy semblance; an unsubstantial image; a phantom; a glimmering.
• noun A false image formed in a telescope, camera, or other optical device by reflection from the surfaces of one or more lenses.