Ñ - Born and brought up in Spanish

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Question: Where did the Ñ come from?
Answer: As you could probably guess, the ñ came originally from the letter n. The ñ does not exist in Latin and is the only Spanish letter of Spanish origins.

Beginning in about the 12th century, Spanish scribes (whose job it was to copy documents by hand) used the tilde placed over letters to indicate that a letter was doubled (so that, for example, nn became ñ and aa became ã). I'm not sure why they used the tilde, except perhaps that it was quick to write, although it may be no coincidence that it is shaped vaguely like an N. The tilde was used not only with the n but with other letters as well.

The popularity of the tilde for other letters eventually waned, and by the 14th century, the ñ was the only place it was used. Its origins can be seen in a word such as año (which means "year"), as it comes from the Latin word annus with a double n. As the phonetic nature of Spanish became solidified, the ñ came to be used for its sound, not just for words with an nn. A number of Spanish words, such as señal and campaña, that are English cognates use the ñ where English uses "gn," such as in "signal" and "campaign," respectively.

The Spanish ñ has been copied by two other languages that are spoken by minorities in Spain. It is used in Euskara, the Basque language that is unrelated to Spanish, to represent approximately the same sound as it has in Spanish. It is also used in Galician, a language similar to Portuguese. (Portuguese uses nh to represent the same sound.)

Additionally, three centuries of Spanish colonial rule in the Philippines led to the adoption of many Spanish words in the national language, Tagalog (also known as Pilipino or Filipino). The ñ is among the letters that have been added to the traditional 20 letters of the language.

And while the ñ isn't part of the English alphabet, it frequently is used by careful writers when using adopted words such as jalapeño, piña colada or piñata and in the spelling of various personal and place names.

In Portuguese, the tilde is placed over vowels to indicate that the sound is nasalized. That use of the tilde has no apparent direct connection with the use of the tilde in Spanish.

Fuente: http://spanish.about.com/cs/historyofspanish/f/tilde_origins.htm