Witch is a very old word meaning "magic-maker", from a root which meant "bending" and "shaping". For many of us, the word Witch is a powerful reclaiming of that inherent human power to make changes around us. For others, including some of the people within Wicca, that word is not their word. Some people within Wicca take the adjective "Wiccan" and use it as a noun.
(Some people question the authenticity of the etymology that says "witch" means "to bend or shape." They believe that the word is simply from the Old English for "wise one" and has no relation to the root mentioned above -- which gives us the modern word "wicker," for instance. However, this definition is a good way to think of how a modern Witch might see him/herself.)