American dictionary of the English language

The pen may be stronger than the sword, but if all else fails you can assault an attacker with this hefty volume. Did you know that there are twenty different definitions for “to”? This is a must-have for any historical writer, to see what words were used in the old days and to see sentence examples with each word. There's even a hefty section on grammar and how to use words properly. (Humorous observation: Webster believed “doesn't” was bad form and advised the use of “don't” instead: “She don't think that I should leap the fence.” I saw this use in a Susan Warner book and thought it a typo, but apparently not.)

A great peek at word use in America in the 1800s and a resource I have used many times.