English is primarily a descendant of Germanic languages, but it contains many words borrowed from Greek. These words tend to relate to the abstract realms of philosophy and ideas. In fact, the words "idea" and "philosophy" themselves are Greek.
The words of Greek origin used as part of English vocabulary were brought in through literature, scripture and texts. Some Greek words first joined Latin texts and eventually entered English because Latin was the written currency in medieval and Renaissance Europe. Latin was also the language of the Catholic religion, which created many written works.
The Greek language contributes many prefixes and suffixes to English; the "tele" of telephone and telescope; the "eu" in euthanasia; the prefix words "anti-" and "pro-"; and the suffix "-ic," as in fanatic. The English language contains words of a variety of origins, and some words contain particles of Greek and non-Greek words. An example is "television," which pairs Greek "tele" with Latin "vision." Other words meld Greek prefixes and Greek roots to create neologisms of Greek words formed by English speakers. Some examples are "zoology" and "utopia."
Approximately 5 percent of English words in a standard dictionary of 80,000 words are of Greek origin, according to Wikipedia.