OneLook crawls and indexes the headwords from ~1000 online dictionaries and glossaries. When you do a wildcard search, it searches all of these lists at once.

OneLook crawls and indexes the headwords from ~1000 online dictionaries and glossaries. When you do a wildcard search, it searches all of these lists at once. Clicking on one of the results will show you the sources. The sites range from small subject-specific glossaries with a few dozen words, to commercial dictionaries like Merriam-Webster and OED.