About 80 percent of the entries in any English dictionary are borrowed, mainly from Latin. Over 60 percent of all English words have Greek or Latin roots. In the vocabulary of the sciences and technology, the figure rises to over 90 percent. About 10 percent of the Latin vocabulary has found its way directly into English without an intermediary (usually French). For a time the whole Latin lexicon became potentially English and many words were coined on the basis of Latin precedent. Words of Greek origin have generally entered English in one of three ways: 1) indirectly by way of Latin, 2) borrowed directly from Greek writers, or 3) especially in the case of scientific terms, formed in modern times by combining Greek elements in new ways. The direct influence of the classical languages began with the Renaissance and has continued ever since. Even today, Latin and Greek roots are the chief source for English words in science and technology.
So this is great for Italian students of English because right at the start they already know almost 80% of the entire English vocabulary (wink wink!). So then why is it that when they speaking with English speakers they understand almost nothing and are totally not understood?
That is because the English pronunciation of Latin words arecompletely different from the Italian. Take the example of psychology pronounced as /saɪˈkɒlədʒi/ (http://dictionary.reference.com/browse/psychology) rather than /'psɪkolo'dʒia/ as in Italian. So when a student who doesn't know the correct pronunciation of the English word hears it from a native speaker will not recognize it although he knows the word perfectly well from his/her own language.
You don't know a word until you know how to pronounce it! Use online dicitionaries such as the one in the above link to always check and double check, listen to and repeat a word, until you know it.