42. One or more computer-readable storage media encoded with instructions that, when executed, cause a processor to perform acts comprising: receiving, via a network connection, a threshold parameter indicating a predetermined threshold similarity of subject matter and an input document associated with a new item available for purchase, the input document to be indexed into a search index file; comparing a subject matter of the input document to a subject matter of an existing document that relates to an item available for purchase and is already indexed into the search index file, wherein the structure of the input document includes at least two fields, the at least two fields each including content, and the predetermined threshold similarity of subject matter exists at least when a percentage of fields in a structure of the input document correspond to fields in a structure of the existing document; determining, based at least on the comparison, that the input document and the existing document meet the predetermined threshold similarity of subject matter; responsive to determining that the input document and the existing document meet the predetermined threshold similarity of subject matter, identifying text in the input document that is dissimilar to text in the existing document; designating any dissimilar text between the input document and the existing document as candidate synonyms; merging the candidate synonyms into the search index file, wherein the merging associates the dissimilar text as synonyms in the search index file; and indexing the input document into the search index file.
42. One or more computer-readable storage media encoded with instructions that, when executed, cause a processor to perform acts comprising: receiving, via a network connection, a threshold parameter indicating a predetermined threshold similarity of subject matter and an input document associated with a new item available for purchase, the input document to be indexed into a search index file; comparing a subject matter of the input document to a subject matter of an existing document that relates to an item available for purchase and is already indexed into the search index file, wherein the structure of the input document includes at least two fields, the at least two fields each including content, and the predetermined threshold similarity of subject matter exists at least when a percentage of fields in a structure of the input document correspond to fields in a structure of the existing document; determining, based at least on the comparison, that the input document and the existing document meet the predetermined threshold similarity of subject matter; responsive to determining that the input document and the existing document meet the predetermined threshold similarity of subject matter, identifying text in the input document that is dissimilar to text in the existing document; designating any dissimilar text between the input document and the existing document as candidate synonyms; merging the candidate synonyms into the search index file, wherein the merging associates the dissimilar text as synonyms in the search index file; and indexing the input document into the search index file. 44. The one or more computer-readable storage media of claim 42 , wherein the comparing includes comparing text of the input document to text of the existing document.