a diacritical mark (~) placed over the letter n in Spanish to indicate a palatal nasal sound or over a vowel in Portuguese to indicate nasalization
source: WordNet 3.0
The accentual mark placed over n, and sometimes over l, in Spanish words [thus, ñ, <ilde;], indicating that, in pronunciation, the sound of the following vowel is to be preceded by that of the initial, or consonantal, y.