7. A computer program product for supporting acquisition of information from a document including a plurality of words, the computer program product comprising a computer readable storage medium having program code embodied therewith, the program code readable and executable by a processor to the method comprising: acquiring first information that shows a degree to which the document belongs to each of a plurality of clusters based on a concept included in the document, and second information that shows a degree to which a single word among the plurality of words appears in each of the plurality of clusters based on a concept of the single word; generating third information that shows a degree of overlap between the concept included in the document and the concept of the single word, based on the first information and the second information; determining whether or not the third information shows a degree of overlap that is lower than a predetermined criterion; outputting information indicating that the single word is a unique word in the document in response to determining that the third information shows the degree of overlap is lower than the predetermined criterion, wherein the unique word is a word that is found only in the document that belongs to one or more of the plurality of clusters, and wherein the document is a single document; retrieving the document that contains the unique word; extracting words from each document of the plurality of documents, wherein, with respect to the plurality of documents, by performing clustering using words extracted from each document, acquiring a first probability that is a probability that the document belongs to the plurality of clusters, respectively, as the first information, and acquiring a second probability that is a probability that the single word belongs to the plurality of clusters, respectively, as the second information; calculating a sum total of products of the first probability with respect to a single cluster among the plurality of clusters and the second probability with respect to the single cluster for all clusters of the plurality of clusters; and generating the sum total as the third information.
7. A computer program product for supporting acquisition of information from a document including a plurality of words, the computer program product comprising a computer readable storage medium having program code embodied therewith, the program code readable and executable by a processor to the method comprising: acquiring first information that shows a degree to which the document belongs to each of a plurality of clusters based on a concept included in the document, and second information that shows a degree to which a single word among the plurality of words appears in each of the plurality of clusters based on a concept of the single word; generating third information that shows a degree of overlap between the concept included in the document and the concept of the single word, based on the first information and the second information; determining whether or not the third information shows a degree of overlap that is lower than a predetermined criterion; outputting information indicating that the single word is a unique word in the document in response to determining that the third information shows the degree of overlap is lower than the predetermined criterion, wherein the unique word is a word that is found only in the document that belongs to one or more of the plurality of clusters, and wherein the document is a single document; retrieving the document that contains the unique word; extracting words from each document of the plurality of documents, wherein, with respect to the plurality of documents, by performing clustering using words extracted from each document, acquiring a first probability that is a probability that the document belongs to the plurality of clusters, respectively, as the first information, and acquiring a second probability that is a probability that the single word belongs to the plurality of clusters, respectively, as the second information; calculating a sum total of products of the first probability with respect to a single cluster among the plurality of clusters and the second probability with respect to the single cluster for all clusters of the plurality of clusters; and generating the sum total as the third information. 8. The computer program product of claim 7 , wherein the method further comprises: acquiring the first information and the second information by performing clustering with respect to a plurality of documents that include the document.