Dictionaries
Did you find a thick Webster's dictionary, printed on newsprint, for $2.99, in the supermarket? A bargain?
Probably not. Webster is not a copyrighted name. Anybody can use it--and many do. If you want the Webster's, look for Merriam-Webster's dictionary.
prescriptive and descriptive
Merriam-Webster's is a descriptive dictionary; that is, selection of words is based upon the words actually being used by people.
If you want your dictionary to guide you in the "worthiness" of a word, you may want to choose a different dictionary. (Many linguists are dismissive about prescriptive approaches to language and grammar.)
Merriam-Webster's is nevertheless a fine dictionary. Another you may want to consider is the American Heritage® Dictionary of the English Language.
old dictionary. What's the matter with the dictionary your mother used in college? Nothing--except it probably doesn't have lots of words in it that you want to know. Language changes, and nowadays English seems to be changing at a breakneck pace.