By Anglo-French is meant the highly important form of French which is largely peculiar to England, and is of the highest value to the philologist. The earliest forms of it were Norman, but it was afterwards supplemented by words borrowed from other French dialects, such as those of Anjou and Poitou, as well as from the Central French of Paris. It was thus developed in a way of its own, and must always be considered, in preference to Old Continental French, when English etymologies are in question. It is true that it came to an end about 1400, when it ceased to be spoken; but at an earlier date it was alive and vigorous, and coined its own peculiar forms. A very simple example is our word duty, which certainly was not borrowed from the Old French devoir, but from the Anglo-French duetee, a word familiar in Old London, but absolutely unknown to every form of continental French.
The point which I have here to insist upon is that not only does our literary language abound with Anglo-French words, but that they are also common enough in our dialects; a point which, as far as I know, is almost invariably overlooked. Neither have our dialects escaped the influence of the Central French of Paris, and it would have been strange if they had; for the number of French words in English is really very large. It is not always possible to discriminate between the Old French of France and of England, and I shall here consider both sources together, though the Old Norman words can often be easily discerned by any one who is familiar with the Norman peculiarities. Of such peculiarities I will instance three, by way of example. Thus Anglo-French often employs ei or ey where Old French (i.e. of the continent) has oi or oy; and English has retained the old pronunciations of ch and j. Hence, whilst convoy is borrowed from French, convey is Anglo-French. Machine is French, because the ch is pronounced as sh; but chine, the backbone, is Anglo-French. Rouge is French, because of the peculiar pronunciation of the final ge; but rage is Anglo-French; and jaundice is Anglo-French, as it has the old j. See Chapters III-VI of my Principles of English Etymology, Second Series.