Disambiguation means clustering items by the entities they reference. Examples include figuring out who wrote what, whom a pronoun refers to, and what RNA molecule a short read came from. We focus on author disambiguation. There are $n$ items (mentions of author names) and $O(n)$ clusters (actual authors) to recover. Each mention has a small number of observed attributes, but $O(n)$ attributes are observed in total. The induced similarity matrix is dense. In this setting, standard clustering algorithms either cannot effectively consider essential attributes, or are intractable due to at least quadratic runtime. We propose and evaluate a supervised, $O(n \log n)$ disambiguation procedure based on recursive spectral bipartitioning and an efficient representation of the similarity matrix.