This from Dictionary.com:
et·y·mol·o·gy[et-uh-mol-uh-jee] Show IPA
noun, plural et·y·mol·o·gies.
the derivation of a word. Synonyms: word origin, wordsource, derivation, origin.
a chronological account of the birth and development of aparticular word or element of a word, often delineating itsspread from one language to another and its evolvingchanges in form and meaning. Synonyms: word history,word lore, historical development.
the study of historical linguistic change, especially asmanifested in individual words.
I find etymology helpful in writing my historical fantasy stories. If you take a look at the bottom of the Dictionary.com post above, see the part where it says "Origin?" (I highlighted it in yellow.) All that information is part of etymology. And anytime you look up a word on Dictionary.com, you'll see the origin of the word at the bottom.
Why is this helpful, you ask?
Well, if you're wondering if a certain word was used during the time period of your story, you can find out. Simply look up the word.
More so than Dictionary.com, I prefer to use Etymology Online. Here you can type in any word and it will list the history and give similar words too. For example, I looked up the work "kitchen" and here is one answer:
Another way you can help you word usage if you are writing a time period story is to read book from that time period. It can be fun or frustrating reading historical literature, but it's the best place to see dialogue from your time period. If you're writing medieval, try to read some of Geoffrey Chaucer's The Canterbury Tales. If you're writing regency, read some Jane Austen (This link leads to Persuasion online). If you're writing steampunk, read some Jules Verne (This link leads to Twenty Thousand Leagues Under the Sea online).
Movies are another option. They're sometimes easier, but then you are trusting that the filmmakers did their research, which can be risky.
How about it? If you write in an different era of time, what are some ways that you find accurate dialogue and word usage?