For your information, modern and ancient Greek are not two different languages. It's officially a fact that modern Greek stems directly from the Attic 'koine', with strong elements of words as old as Mycenaean and ancient Greek. Hence ancient Greek has survived in the modern Greek language, in fact it makes up 97% of modern Greek. That makes the Greek language the oldest indoeuropean language with a documented history of at least 3600 years.
Modern Greek, Encyclopedia of the World's Major Languages, BrianJoseph Ancient Greek, Encyclopedia of the World's Major Languages, BrianJoseph Greek Language, Columbia Electronic Encyclopedia. The Perseus Project has many useful pages for the study of classical languages and literatures, including dictionaries. The Greek Language and Linguistics Gateway