For almost thirty years 'The Civil War Dictionary' has been the most complete, authoritative, and handy reference book on what has been called the Second American Revolution, 1861-1865.
Great reference. I read at least one Civil War book a year, used to read a lot more, and this book has always been valuable, especially for biographical info. But why "dictionary"? It's clearly an encyclopedia.
This book is more like a mini-encyclopedia for the war, with brief articles covering generals and the major campaigns, battles, and units. As can be expected for a one volume work, it doesn't go into detail about any single subject, so its usefulness really depends on how much the reader already knows about the war.