Ghost, Specter, Spook

Ghost
 
The word ghost has its origins in the Proto-Indo-European root gheis (excitement, amazement, fear), the source of Proto-Germanic gaistaz (in turn, the source of Old Saxon gest, Dutch geest, German Geist, all meaning spirit or ghost; in particular, the disembodied spirit of a dead person. From these Germanic sources comes Old English gast or gaest (breath; good or bad spirit, angel, demon; person, man, human being; especially as used in the Biblical sense to mean soul, spirit, life) and Old English gaestan (to terrify).
 
In brief, ghost is a Germanic word meaning supernatural being. The related Latin term is spiritus (spirit); e.g., ‘Holy Ghost’ is a Germanic term; ‘Holy Spirit’ is the equivalent Latin term.
 
Ghost, as an English term meaning the spirit of a dead person wandering among the living or haunting them is from the late 14th century. Sounds ghastly.
 
A poltergeist (a noisy spirit or ghost which makes its presence known by noises) is from 1838 from German Poltergeist (literally, ‘noisy ghost’).
 
The words aghast and ghastly (terrified, filled with frightened amazement), from around 1300, are from Middle English agasten (to frighten) and Old English gaest (ghost).
 
Specter
 
From around 1600, meaning a frightening ghost, from Latin spectrum (appearance, vision, apparition). Specter as an object of dread is from 1774.
 
Spook
 
Spook is first seen in English in 1801, meaning specter, apparition, ghost, from Dutch spook, Middle Dutch spooc (spook, ghost), German Spuk (ghost, apparition), and other Germanic words. The original root of the word is unknown. Spooky, meaning frightening, is from 1854. The verb ‘to spook’ meaning to unnerve is from 1935.
 
Reference: Online Etymological Dictionary, https://www.etymonline.com/
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