21. The apparatus of claim 20 wherein the cluster label comprises a plurality of word senses and the processing circuitry is configured to select one of the word senses to disambiguate the cluster label.
26. The apparatus of claim 21 wherein the processing circuitry is configured to identify the documents of the subset using the terms occurring in the documents of the subset, and wherein the processing circuitry is configured to determine, for individual ones of the word senses, a plurality of semantic similarity values with respect to the terms to select the one of the word senses.