Does anyone know of a website or book on French language word families, something along the line of Howard Keller's German Word Family Dictionary? I'm interested in French word roots and the verbs, adjectives, nouns, and adverbs that contain them, for my study of French vocabulary. I've been googling away for a couple days, but can't seem to find anything fitting the bill.
I do not know the special book that fulfils your need.
The majority of French words derive from Vulgar Latin or were constructed from Latin or Greek roots. In many cases a single etymological root appears in French in a "popular" or native form, inherited from Vulgar Latin, and a learned form, borrowed later from Classical Latin. (Wikipedia)
Looking in a Latin/Greek dictionary will help you to find "root words" in French.
Moreover, if you already know a Latin based language you can try to guess from its vocabulary.
EDIT : wiktionary often give the etymology of the word and how it was built.
There's the famous Dictionnaire historique de la langue française by Alain Rey. An excellent reference, very useful, and it's quite exactly what you seem to search for.
It could be an expensive book (2 volumes in fact), but I guess it could also be found in some french (public or not) libraries.
Older material; nevertheless, these might provide some insight and are presented more or less in the format you alluded to:
Dictionnaire des racines et derivés de la langue française, dans lequel on trouve tous les mots distribués par famille d'après la similitude de consonnance et de signification, et chaque famille rangée dans l'ordre abécédaire de la racine dont elle dépend, Charrassin, Frédéric; François, Ferdinand, ed. Grassart, 1900
Dictionnaire étymologique de la langue françoise, où les mots sont classés par familles ... Jean-Baptiste -Bonaventure de Roquefort, ed. Decourchant, 1829, (also tome deuxième)
Note such works often have "par famille" or "par racines" in their title. Also, something of a curiosity, along the same lines, in English:
The Principal Roots of the French Language: Simplified by a Display of Their Incorporation Into The English Tongue, Hall's, publ. John Taylor, 1826
This looks like the kind of thing you are looking for:
Claude Gruaz (2008). Dictionnaire synchronique des familles dérivationnelles de mots français, Editions Lambert-Lucas.