Etymology
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adder (n.)

Middle English naddre, from Old English (West Saxon) næddre (Mercian nedre, Northumbrian nedra), "a snake; the Serpent in the Garden of Eden," from Proto-Germanic *naethro "a snake" (source also of Old Norse naðra, Middle Dutch nadre, Old High German natra, German Natter, Gothic nadrs), from PIE root *nētr- "snake" (source also of Latin natrix "water snake" (the sense is probably by folk-association with nare "to swim"); Old Irish nathir, Welsh neidr "snake, serpent").

The modern form represents a faulty separation 14c.-16c. of a nadder into an adder, for which see also apron, auger, nickname, orange, humble pie, aitchbone, umpire. Nedder is still a northern English dialect form.

Since Middle English the word has been restricted to use as the common name of the viper, the only poisonous British reptile (though not generally fatal to humans), then by extension it was applied to venomous or similar snakes elsewhere (puff-adder, etc.). Folklore connection with deafness is via Psalms lviii.1-5. The adder is said to stop up its ears to avoid hearing the snake charmer called in to drive it away.

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puff-adder (n.)

1789 of a large South African snake that is venomous; 1882 of a western U.S. snake that is not; from puff (v.) + adder.

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aught (n.2)

"nothing, zero," faulty separation of a naught (see naught). See adder for similar misdivisions.

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nadder (n.)

the earlier form of adder (q.v.). Also see N.

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auger (n.)

"instrument for boring larger holes," c. 1500, a faulty separation of Middle English a nauger, from Old English nafogar "nave (of a wheel) drill," from Proto-Germanic *nabo-gaizaz (source also of Old Norse nafarr, Old Saxon nabuger, Old High German nabuger), a compound whose first element is related to nave (n.2) and whose second is identical to Old English gar "a spear, borer" (see gar). For similar misdivisions, see adder. The same change took place in Dutch (avegaar, egger).

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deaf (adj.)

Old English deaf "lacking the sense of hearing," also "empty, barren," from Proto-Germanic *daubaz (source also of Old Saxon dof, Old Norse daufr, Old Frisian daf, Dutch doof "deaf," German taub, Gothic daufs "deaf, insensate"), from PIE dheubh-, which was used to form words meaning "confusion, stupefaction, dizziness" (source also of Greek typhlos "blind," typhein "to make smoke;" Old English dumb "unable to speak;" Old High German tumb).

The word was pronounced to rhyme with reef until 18c. Meaning "refusing to listen or hear" is from c. 1200. As a noun, "deaf persons," from c. 1200. Deaf-mute is from 1837, after French sourd-muet. Deaf-mutes were sought after in 18c.-19c. Britain as fortune-tellers. Deaf as an adder (Old English) is from Psalms lviii.5 (see adder).

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viper (n.)

early 15c., from Old French vipere, earlier in English as vipera (c. 1200), directly from Latin vipera "viper, snake, serpent," contraction of *vivipera, from vivus "alive, living" (from PIE root *gwei- "to live") + parire "bring forth, bear" (from PIE root *pere- (1) "to produce, bring forth"). In common with many snake species in cooler climates, in most cases the viper's eggs are kept inside the mother until hatching.

Applied to persons of spiteful character at least since 1590s. The only venomous snake found in Great Britain, but not especially dangerous. The word replaced native adder. "The flesh of the viper was formerly regarded as possessing great nutritive or restorative properties, and was frequently used medicinally" [OED]; hence viper-wine, wine medicated with some kind of extract from vipers, used 17c. by "gray-bearded gallants" in a bid "to feele new lust, and youthfull flames agin." [Massinger]

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apron (n.)

"apparel for covering the front of a person" (especially while at work, to keep clothes clean), mid-15c., faulty separation (as also in adder, auger, umpire) of a napron (c. 1300), from Old French naperon "small table-cloth," diminutive of nappe "cloth," from Latin mappa "napkin." Napron was still in use late 16c. The shift of Latin -m- to -n- was a tendency in Old French (conter from computare, printemps from primum, natte "mat, matting," from matta).

The word was extended 17c. to things which resemble or function like an apron. It has been symbolic of "a wife's business" from 1610s; apron-string tenure in old law was in reference to property held in virtue of one's wife, or during her lifetime only.

Even at his age, he ought not to be always tied to his mother's apron string. [Anne Brontë, "The Tenant of Wildfell Hall," 1848]
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snake (n.)

Old English snaca, from Proto-Germanic *snakon (source also of Old Norse snakr "snake," Swedish snok, German Schnake "ring snake"), from PIE root *sneg- "to crawl, creeping thing" (source also of Old Irish snaighim "to creep," Lithuanian snakė "snail," Old High German snahhan "to creep"). In Modern English, gradually replacing serpent in popular use.

Traditionally applied to the British serpent, as distinguished from the poisonous adder. Meaning "treacherous person" first recorded 1580s (compare Old Church Slavonic gadu "reptile," gadinu "foul, hateful"). Applied from 17c. to various snake-like devices and appliances. Snakes! as an exclamation is from 1839.

Snake eyes in crap-shooting sense is from 1919. Snake-bitten "unlucky" is sports slang from 1957, from a literal sense, perhaps suggesting one doomed by being poisoned. The game of Snakes and Ladders is attested from 1907. Snake charmer is from 1813. Snake pit is from 1883, as a supposed primitive test of truth or courage; figurative sense is from 1941. Phrase snake in the grass is from Virgil's Latet anguis in herba [Ecl. III:93].

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N 

fourteenth letter of the English alphabet; in chemistry, the symbol for nitrogen.

In late Middle English a and an commonly were joined to the following noun, if that word began with a vowel, which caused confusion over how such words ought to be divided when written separately. In nickname, newt, and British dialectal naunt, the -n- belongs to a preceding indefinite article an or possessive pronoun mine.

Other examples of this from Middle English manuscripts include a neilond ("an island," early 13c.), a narawe ("an arrow," c. 1400), a nox ("an ox," c. 1400), a noke ("an oak," early 15c.), a nappyle ("an apple," early 15c.), a negge ("an egg," 15c.), a nynche ("an inch," c. 1400), a nostryche ("an ostrich," c. 1500). My naunt for mine aunt is recorded from 13c.-17c. None other could be no noder (mid-15c.). My nown (for mine own) was frequent 15c.-18c. In 16c., an idiot sometimes became a nidiot (1530s), which, with still-common casual pronunciation, became nidget (1570s), now, alas, no longer whinnying with us.

It is "of constant recurrence" in the 15c. vocabularies, according to Thomas Wright, their modern editor. One has, among many others, Hoc alphabetum ... a nabse, from misdivision of an ABC (and pronouncing it as a word), and Hic culus ... a ners. Also compare nonce, pigsney. Even in 19c. provincial English and U.S., noration (from an oration) was "a speech; a rumor."

The process also worked in surnames, from oblique cases of Old English at "by, near," as in Nock/Nokes/Noaks from atten Oke "by the oak;" Nye from atten ye "near the lowland;" and see Nashville. (Elision of the vowel of the definite article also took place and was standard in Chancery English of the 15c.: þarchebisshop for "the archbishop," thorient for "the orient.")

But it is more common for an English word to lose an -n- to a preceding a: apron, auger, adder, umpire, humble pie, etc. By a related error in Elizabethan English, natomy or atomy was common for anatomy, noyance (annoyance) and noying (adj.) turn up 14c.-17c., and Marlowe (1590) has Natolian for Anatolian.  The tendency is not limited to English: compare Luxor, jade (n.1), lute, omelet, and Modern Greek mera for hēmera, the first syllable being confused with the article.

The mathematical use of n for "an indefinite number" is attested by 1717 in phrases such as to the nth power (see nth). In Middle English n. was written in form documents to indicate an unspecified name of a person to be supplied by the speaker or reader.

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