littera

Littera, litterae, f., first declension, and the number changes the meaning, which is the one thing to take away. In the singular a littera is a single character of the alphabet. In the plural, litterae is a letter you send, or writing and learning in general. So litteras mittere is to send a message, not to post the alphabet, and homo litterarum is a scholar.

Medieval scribes very often write a single t, litera, and both spellings sit side by side in this corpus. Ad litteram means literally, in the strict sense of the written characters. From it come litteratus, "lettered", and English letter, literal, literature, literacy and obliterate, which is to strike the letters out.