The period from 500 to 1100 AD is known as the Anglo-Saxon or Old English period of the language. Our most frequent terms of conversation come from this period. However, many of the words of Old English have fallen out of use, so that to a modern reader Old English reads much like a foreign language. William and his followers attempted to impose their language onto the English, but the graft was eventually rejected. Nevertheless many French terms were incorporated into the English language during this time.
Etymology is the study of the history of words.
Many of the words of human biology have colorful histories, and an awareness of these hidden meanings can help us remember the current applications of these terms. If you were having eye problems you would probably go to an eye doctor. If you peruse different textbooks or speak with different professionals you will find that a word that means one thing to one professional may be used a bit differently by another. Even more variations are found among professionals in the pronunciation of words. Keep in mind as we study the terminology of human biology and medicine that our goal is to maximize the probability of success of our communication, and not to learn the absolutely correct and forever unchanging meaning and pronunciation of terms.