bedrick has correctly pointed out that there is widespread confusion between evolution and
natural selection. It is also confused with
Darwinism.
'Evolution' is an old word, and a plain English word meaning development, unrolling, or increasing complexity. The Webster definitions hint at some of this as much as Webster ever reveals any meaning mutter.
Darwin's theory of evolution is so familiar now, and has been applied so widely, that it seems natural to think of evolution as Darwinian evolution. But really all it means is 'change' in some expanding way. So the solar system has evolved. The English language has evolved. These do not imply that any natural selection, or any analogous process such as artificial selection, has taken place.
The evolution of organisms is an old idea; it might well go back to the Greeks, though I can't think of specific instances: it would be a characteristically Epicurean idea, for one. In modern times Erasmus Darwin and Lamarck put forward theories of evolution. A lot of people before (Charles) Darwin believed that species evolved from other species. They just didn't know how.
(An added confusion is that before Charles Darwin the word was also used for an entirely different theory, Webster's 6.(b), which no-one believes in any more.)
The radically new theory, discovered independently first by Patrick Matthew, then by Charles Darwin, then by Alfred Russel Wallace, was a theory of how evolution occurred. They came up with the idea of natural selection. Their idea is now known to be true, and Lamarck's idea of how evolution occurs is known to be false.
And to round off, Darwinism is this combination: that evolution occurs by means of natural selection; what we may also call "Darwinian evolution".
Gorgonzola has pointed out that in modern scientific discussion the word Darwinism is sometimes used more narrowly, with the added sense of gradualism. This is particularly the case with the Stephen Jay Gould camp who attack more orthodox Neo-Darwinism. But Darwin himself was not committed to gradualism, which was a term in nineteenth-century geology opposed to catastrophism. He phrased his arguments in gradualist terms to emphasize how slight the change needed to explain evolution was.