Etymology
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fear (n.)

Middle English fere, from Old English fær "calamity, sudden danger, peril, sudden attack," from Proto-Germanic *feraz "danger" (source also of Old Saxon far "ambush," Old Norse far "harm, distress, deception," Dutch gevaar, German Gefahr "danger"), from PIE *pēr-, a lengthened form of the verbal root *per- (3) "to try, risk."

The sense of "state of being afraid, uneasiness caused by possible danger" developed by late 12c. Some Old English words for "fear" as we now use it were fyrhto, fyrhto; as a verb, ondrædan. Meaning "feeling of dread and reverence for God" is from c. 1400. To put the fear of God (into someone) "intimidate, cause to cower" is by 1888, from the common religious phrase; the extended use was often at first in colonial contexts:

Thus then we seek to put "the fear of God" into the natives at the point of the bayonet, and excuse ourselves for the bloody work on the plea of the benefits which we intend to confer afterwards. [Felix Adler, "The Religion of Duty," 1905]
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fear (v.)
Old English færan "to terrify, frighten," from a Proto-Germanic verbal form of the root of fear (n.). Cognates: Old Saxon faron "to lie in wait," Middle Dutch vaeren "to fear," Old High German faren "to plot against," Old Norse færa "to taunt."

Originally transitive in English; long obsolete in this sense but somewhat revived in digital gaming via "fear" spells, which matches the old sense "drive away by fear," attested early 15c. Meaning "feel fear" is late 14c. Related: Feared; fearing.
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fearless (adj.)
early 15c., from fear (n.) + -less. Related: Fearlessly; fearlessness.
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fearsome (adj.)
"causing fear," 1768, from fear (n.) + -some (1). Occasionally used badly in the sense "timid," which ought to stick to fearful. Related: Fearsomely; fearsomeness.
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God-fearing (adj.)
"reverencing and obeying God," 1759, from God + fearing, present-participle adjective from fear (v.). Old English in the same sense had godfyrht.
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fearful (adj.)
mid-14c., "causing fear," from fear (n.) + -ful. Meaning "full of fear, timid" (now less common) also is from mid-14c. As a mere emphatic, from 1630s. Related: Fearfully; fearfulness.
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afeared (adj.)
Old English afæred, past participle of now-obsolete afear (Old English afæran) "terrify, cause to fear," from a- (1) + færan (see fear (v.)). Used frequently by Shakespeare, but supplanted in literary English after 1700 by afraid (q.v.), to which it has no connection. It survived in popular speech and colloquial writing.
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fright (n.)
Middle English freiht, fright, from Old English (Northumbrian) fryhto, metathesis of Old English fyrhtu "fear, dread, trembling, horrible sight," from Proto-Germanic *furkhtaz "afraid" (source also of Old Saxon forhta, Old Frisian fruchte, Old High German forhta, German Furcht, Gothic faurhtei "fear"). Not etymologically related to the word fear, which superseded it 13c. as the principal word except in cases of sudden terror. For spelling evolution, see fight (v.).
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*per- (3)

Proto-Indo-European root meaning "to try, risk," an extended sense from root *per- (1) "forward," via the notion of "to lead across, press forward."

It forms all or part of: empiric; empirical; experience; experiment; expert; fear; parlous; peril; perilous; pirate.

It is the hypothetical source of/evidence for its existence is provided by: Latin experiri "to try," periculum "trial, risk, danger;" Greek peira "trial, attempt, experience," empeiros "experienced;" Old Irish aire "vigilance;" Old English fær "calamity, sudden danger, peril, sudden attack," German Gefahr "danger," Gothic ferja "watcher.

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arachnophobia (n.)
"morbid fear of spiders," 1925, from combining form of arachnid + -phobia "fear."
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