diacritic
noun
ˌdaɪəˈkrɪtɪk 
ˌdaɪəˈkrɪtɪk a mark such as an accent, placed over, under or through a letter in some languages, to show that the letter should be pronounced in a different way from the same letter without a mark
diacritical ˌdaɪəˈkrɪtɪkl ˌdaɪəˈkrɪtɪkl 