Is that meant to be a question ishana? If so, then yes, mutton is an English word. I don't know about Sri Lanka but in India it refers to the meat of a goat; whereas, in Britain, it's the meat of a sheep.
Mutton was quite common in my youth, but it seems to have disappeared these days. I don't know if this is because we eat more lamb, and all the young animals are killed before they get old enough to be served up as mutton.