In the singular, 'littera' is a character/single letter (e.g., 'a'). Normally, Romans used the plural ('litterae' - or other forms for other cases) to mean a do

In the singular, 'littera' is a character/single letter (e.g., 'a'). Normally, Romans used the plural ('litterae' - or other forms for other cases) to mean a document of some kind.