A program to recognize and reward our most engaged community members
... if you're trying to calculate the distance between terms, and not documents, then I would look into the Levenshtein Edit Distance, which I believe, is not (yet) implemented in RapidMiner.
SimMetrics is an open source extensible library of Similarity or Distance Metrics, e.g. Levenshtein Distance, L2 Distance, Cosine Similarity, Jaccard Similarity etc etc. SimMetrics provides a library of float based similarity measures between String Data as well as the typical unnormalised metric output. It is intended for researchers in information integration, II, and other related fields. It includes a range of similarity measures from a variety of communities, including statistics, DNA analysis, artificial intelligence, information retrieval, and databases.