The Norman invasion of England in 1066 had a major impact not only on the country, but also on the English language. William the Conqueror and his merry band of Normans brought with them Norman French, which became the language of the court, government and the upper class for the next three centuries. English continued to be used by ordinary people, and Latin was the language of the church.

During the period when Norman French was the dominant language, English was rarely used in writing, and started to change in many ways. Before the conquest English had a much more complex grammar, however 70 or 80 years later, the grammar had become much simpler. This change is known as the transformation from Old English to Middle English. At the same time Norman French became Anglo-Norman as it was itself affected by English.

More than 10,000 French words found their way into English – words associated with government, law, art, literature, food, and many other aspects of life. About three quarters of these words are still used, and words derived directly or indirectly from French now account for more than a third of English vocabulary. In fact English speakers know around 15,000 French words, even before they start learning the language.

Quite a lot of the words of French origin used in English sit alongside native English ones, and in some cases there are words of Latin and/or Greek origin with similar meanings. Beef (from French boeuf) is meat from a cow (from Old English cu), a type of bovine (from Latin bovinus via French bovin). A king (from Old English cyning) can be kingly, royal (from French roial) and regal (from Latin regalis).

In some cases words with the same or similar meanings were borrowed from both Norman French and Parisian French at different times. For example warden comes from Norman French, while guardian comes from Parisian French.

The pronunciation of English changed to some extent under the influence of French, as did the spelling. For example, the Old English spellings cw, sc and c became qu, sh and ch, so we now write queen rather than cwen, ship rather than scip, and should rather than scolde.

English grammar did take on a few French structures, such as putting in adjectives after nouns in some expressions – attorney general, secretary general, surgeon general.

Source: http://www.cactusworldwide.com/blog/2012/11/15/the-influence-of-french-on-the-english-language/

Thank you very much agai, Marwah for your comprehensive interesting answer. Hazim.