Phrase Finder
From the Phrasefinder website:
"The Phrasefinder site was founded in 1997 by Gary Martin, who writes the Meaning and Origins section of the site and the Phrase A Week posts. It grew out of an interest in computational linguistics that was developed during his post-graduate research in 1985 and later while working in an IBM-financed research project at Sheffield Hallam University. That project, headed by Prof. Asher Cashdan, investigated the use of artificial intelligence techniques to aid the teaching of writing.In 1998 a listing of the meanings and origins of phrases was added. That list of idioms and phrases now contains more than 1,400 entries (Jan 2006).
Late in 1998 a discussion forum was added. That's a public forum where anyone can ask questions on the meaning or origin of phrases and sayings in English. It now contains an archive of 44,000 questions and answers and continues to grow. The majority of the posted replies have been contributed by a hard-working and exceedingly persistent group of unpaid enthusiasts, some of whom have been contributing daily since early 1999. The ongoing success of the forum is due to them."