Are there resources or tools for "reverse etymology"?

This can be achieved with a touch of Google-fu.

We want to limit our Google search to search only the site, http://www.etymonline.com/.

From reading the url structure of each result, we notice that definitions all contain ?term=, so can we refine the search with these bits of info:

site:etymonline.com inurl:term

Then, we add a space and the term we are looking for; if it appears in the text describing a word's etymology, we have a hit.

For example, we'd type the following if we wanted to search for phagos:

site:etymonline.com inurl:term phagos

Search results for "phagos"

We are a touch limited in that we must rely on the definitions containing that particular variant. For example, the above search returns 5 hits; however, a search for phagous returns 13 hits despite phagos and phagous sharing a common root.

Hope that helps!

EDIT: I've further played with this and noticed that occasionally it returns search pages which don't really add much.

These can be filtered out as they all contain the expression ?search=, so we can use:

site:etymonline.com inurl:term -inurl:search phagos

For anyone interested in understanding how that works, prepending a - negates the statement so -inurl:search evaluates to AND url does not contain "search".

Wiktionary maintains descendant lists, but they are far from complete. See e.g.:

• cornu (Latin)
• wódr̥ (PIE)
• watōr (Proto-Germanic)

Not online, but I picked up a second-hand copy of Pokorný's Indo-European Dictionary some years ago, and I often refer to it for this. I'm sure that scholarship has moved on since, though.

The American Heritage Dictionary (used to be online, no more) had great etymology links back to the root of a word, which then had a link to all the words derived from the root. (so you could go backward and forwards in time).

Those old pages are available through the 'wayback machine' at

http://web.archive.org/web/20080209175233/www.bartleby.com/61/

AHD (at that archive site) also has accompanying articles for Indo-European and Semitic roots, and lists of those roots which then link forward to derivatives:

http://web.archive.org/web/20080211183126/www.bartleby.com/61/IEroots.html

Seems to be slow, but likely to be exactly what you want.

(A comment points out that the dictionary is still online, but it just doesn't offer the same list of IE roots or clickable etymology.)