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 manuscript from c. 1500 has a nylle for "an isle." My naunt for mine aunt is recorded from 13c.-17c. Natomy or atomy was common in Elizabethan English for anatomy. In 16c., an idiot sometimes became a nidiot, which, with still-common casual pronunciation, became nidget, which, alas, has not survived. Marlowe (1590) has Natolian for Anatolian. Also compare nonce.
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.")
But it is more common for an English word to lose an -n- to a preceding a: apron, auger, adder, umpire, humble pie, etc.
The mathematical use of n for "an indefinite number" is first recorded 1852, in to the nth power. 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.