A tittle, meaning “a very small part” refers to a small stroke or point in writing or printing. In Latin this applied to any accent over a letter, but is now most commonly used as the name for the dot over the letter ‘i’. It is also the name of the dots on dice. In medieval calligraphy the tittle was written much larger and it wasn’t until the fixed typeface printing was introduced in the 15th century, the tittle became smaller. The use of the word ‘dot’ did not begin until the 18th century.
A jot on the other hand, is the name of the smallest part of a piece of writing. It is the Anglicized version of the Greek iota – the smallest letter of the Greek alphabet, which corresponds to the Roman ‘i’. This, in turn, was derived from the Hebrew word jod, or yodr, which is the the smallest letter of the square Hebrew alphabet. Today, we use the word jot more generally to mean ‘a tiny amount’. For example, when we need to write a short note, we ‘jot it down’. (merriam-webster, phrases.org.uk)