1. A method for updating a dictionary in a dictionary updating system with an unregistered word not registered in the dictionary, the method comprising: extracting a document of interest of a user in each predetermined extraction period from a predetermined server connected to the dictionary updating system through a network, and extracting candidate unregistered words existing in the extracted document according to predetermined unregistered word extraction rules; extracting unregistered words among the candidate unregistered words and extracting candidate semantic classes of the unregistered words based on information on appearance frequencies of the candidate unregistered words retrieved from the document; verifying the unregistered words according to a predetermined unregistered word verification method and determining semantic classes of the verified unregistered words with usage examples of the unregistered words obtained through a searching unit; updating a first dictionary of the dictionary updating system by registering all of the verified unregistered words and the semantic classes of the verified unregistered words; and re-registering, in a second dictionary of the dictionary updating system, registered words among registered words registered in the first dictionary, based on the user's usage frequency of the registered words and appearance frequency information in a document of the registered words, wherein registered words registered in the second dictionary are retrieved prior to registered words registered in only the first dictionary.