Discussion Forum—A Way with Words, a fun radio show and podcast about language

Your best bet will be, beyond doubt, the Oxford English Dictionary. It provides good historical citations of meaning as it has changed over time. Online access is about $300 a year, but you may well find that your local library offers free access. Some libraries will even allow access remotely over the Internet, using a login and password that they have assigned you. I would not recommend the print edition, as it is now out of date.

Regarding the use of dictionaries at all for historical writing: be careful! There are two traps to avoid.

One, the overuse of period vocabulary and lexicon can make it difficult for your modern readers to enjoy your work. Few readers will expect your narrative portions to contain only historically accurate terms, so your best bet is to make sure your dialog is free of anachronisms and yet, at the same time, not overloaded with colorful expressions from the past. A few terms here and there will do the trick. Diana Gabaldon does this pretty well in her Outlabder novels. She makes little effort to render Scots in a spelling that indicates pronunciation, but she'll leave out obviously modern words and throw in words like “Sassenach” here and there and make cultural and political references that give a fairly decent wash of color to her scene. Of course, her work involves time travel, so if she slips up the reader can just assume that a modern character taught the out of place words to the historical ones.

Two, vocabulary is only part of the character of language and dictionaries make mistakes: they can offer only a vague portrait of it in a certain time and a place. Your best bet is to read literature written during the period you are writing about (in your case, in French and English), or else read nonfiction that covers the period you are writing about. You will soon get a feel for the “temperature” of the era, meaning that you will begin to intuitively understand the manners, mores, class, politics, and so on, of the age, and you will begin to get a feel of how they are reflected in the prosody, register, politeness, and pragmatics of speech. Language is more than lexis, as all good translators will tell you.

Whenever I'm asked a question like yours, I always recall a Henning Mankell novel I read. It was translated from Swedish. The translator, unfortunately, mistranslated the Swedish greeting “hej.” In English it means “hi,” “hello,” “hey,” and so forth, depending on the situation. But the translator decided that it should be “Hi!” in most cases. Including the exclamation mark. So the book ends up with absurdities like a dour detective coming into the office after a long night on a case, with dialog that has him greeting others with a cheery, inane “Hi!” instead of something like a curt “hey.” It was just the wrong tone.

The reason I recommend the OED is specifically because it includes more language from the period you're writing about and because of the historical citations. The Shorter has little of those. It is not really useful for your purposes.

Same for a dictionary of etymology: you need citations, not etymologies.

The Online Etymology Dictionary is fine only if you do not intend to cite it, quote it, nor use its contents in a legal, business, or scholarly document. It's a mish-mash of information borrowed and rewritten from other sources, some reliable, some not, with little effort to verify, substantiate, or further investigate. In short, it is mainly useful only when an approximate answer will suffice.