20,000. It has been estimated, that every tenth word was an 'invention'. Usually from Latin, or sometimes Greek. "Titus Andronicus, was entirely written in Latin! Shakespeare would listen to his playwright friends in the London taverns at night, as, with their classical education, they would 'invent' words from the Latin roots, a talent he quickly developed to give us, 'drug', 'film', 'advertising', 'zany', 'fashionable', 'premeditated', 'watchdog', and others so "modern", that new readers, not used to English history, believe him to be writing today!