As an editor of the Random House dictionary and an author of The Dictionary of American Slang, Flexner is especially qualified for this job: a white elephant of American language origins and usage in historical context. Arranged alphabetically, the entries include ethnic groups (Blacks, Indians), historical eras (New Deal, Reconstruction), transportation jargon (for cars, railroads), land forms and common phrases, from the early colonies to dirty tricks and NOW. Some of the group entries are idiosyncratic (""Gumption, Spunk, Grit, Sand, Guts, Balls"" is one) so the index--which lists every word mentioned--is essential. And those who look for four-letter words (""I wonder how many readers will look up these words first,"" begins one entry) will find them too, neutralized but honestly encountered. Accompanied by topical illustrations--newspaper clippings, photographs, advertising logos--they are both lively and informative.