  Dictionaries are inherently circular in nature. A given word is linked to a
set of alternative words (the definition) which in turn point to further
descendants. Iterating through definitions in this way, one typically finds
that definitions loop back upon themselves. The graph formed by such
definitional relations is our object of study. By eliminating those links which
are not in loops, we arrive at a core subgraph of highly connected nodes.
  We observe that definitional loops are conveniently classified by length,
with longer loops usually emerging from semantic misinterpretation. By breaking
the long loops in the graph of the dictionary, we arrive at a set of
disconnected clusters. We find that the words in these clusters constitute
semantic units, and moreover tend to have been introduced into the English
language at similar times, suggesting a possible mechanism for language
evolution.
