The Norman conquest of England in the 11th century gave rise to heavy borrowings from Norman-French, and vocabulary and spelling conventions began to give the superficial appearance of a close relationship with Romance languages to what had now become Middle English. The Great Vowel Shift that began in the south of England in the 15th century is one of the historical events that mark the emergence of Modern English from Middle English.
Owing to the assimilation of words from many other languages throughout history, modern English contains a very large vocabulary. Modern English has not only assimilated words from other European languages but also from all over the world, including words of Hindi and African origin. The Oxford English Dictionary lists over 250,000 distinct words, not including many technical, scientific, or slang terms, or words that belong to multiple word classes.
Extracted from Wikipedia.