A、It lists abbreviations, proper nouns, and tables of measures. B、It is an unabridged edition providing as many as 500,000 entri

Although people often use the phrase "the dictionary", there are many different kinds of dictionaries, some general and some specialized. General dictionaries are all-purpose dictionaries that contain a broad range of words and common usage. The first general dictionary that you used was probably a school dictionary. These dictionaries contain relatively few words and emphasize common words that you are most likely to encounter in your school years.
    Later, most people acquire a college dictionary. These dictionaries have more than 150, 000 entries with detailed definitions that are sufficient for most college students as well as general users. They also separately list abbreviations, biographical and geographical names, foreign words and phrases and tables of measures. The Random House Websters College Dictionary and the American Heritage Dictionary are well-known college dictionaries.
    For scholars or researchers, un abridged dictionary provides as many as 500,000 entries that have detailed definitions and extensive word histories. You will find these dictionaries primarily in libraries and they often spend several volumes. Specialized dictionaries such as the drinking water dictionary or dictionary of legal terms are also very useful for scholars or researchers.