Abstract: A statistical thesaurus is built dynamically, from the same text collection that is being searched, allowing improved generation of expanded query terms. The thesaurus is dynamic in that thesaurus records are collected, ranked, accessed, and applied dynamically. Thesaurus "records" are actually formed as indexed documents arranged in "collections". The collections are preferably distinguished based on text source (court cases versus news wires versus patents, and so forth). Each record has terms assembled in indexed groups (or segments) which inherently reflect a ranking based on relevance to an initial query. After an initial query is received, the appropriate collection(s) of records may be searched by a conventional search and retrieval engine, the searches inherently returning records ranked by degree of relevance due to the record indexing scheme. A record ranking scheme avoids contamination of relevant records by less relevant records.