Specter

google

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early 17th century: from French spectre or Latin spectrum (see spectrum).

wiktionary

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From French spectre, from Latin spectrum(“appearance, apparition”). Doublet of spectrum.

etymonline

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specter (n.)

c. 1600, "frightening ghost," from French spectre "an image, figure, ghost" (16c.), from Latin spectrum "appearance, vision, apparition" (see spectrum). Figurative sense "object of dread" is from 1774.