Norman Lewis was an author, grammarian, lexicographer, and etymologist. Lewis was a leading authority on English-language skills, whose best-selling 30 Days to a More Powerful Vocabulary published by Pocket Books in 1971 promised to teach readers "how to make words your slaves" in fifteen minutes a day.
Other better-known titles included Word Power Made Easy, a vocabulary builder published in 1949, and Roget's New Pocket Thesaurus in Dictionary Form, published in 1961.Lewis told The Times in 1978 that the revised Roget's sold "like mad." At the time, more than five million copies of the pocket thesaurus had been purchased.

Despite his publishing success, Lewis often said that "writing is my job, but teaching is my recreation."Much of Lewis’s work is still in print, including Word Power Made Easy (Pocket Books, 1979); 30 Days to Better English (Signet, 1985); and 30 Days to a More Powerful Vocabulary (Pocket Books, 1971), written with Wilfred Funk. Lewis also edited several editions of Roget’s Thesaurus, including The New Roget’s Thesaurus in Dictionary Form (Berkley, 1976).