The right word can be more than "What's the name for that thing?" Especially when you're writing something from an earlier era. Sometimes when you get caught using a word from the wrong time – an anachronism – no one will notice, and you can tell yourself "It doesn't really make a difference." But sometimes it's enough to jar the reader, if only momentarily, out of the world you've created.
About ten years or so ago some girl (I'm assuming here she couldn't have been more than 17) sent me the first chapter of her pirate romance that started with the female protagonist running in terror from the notorious pirate Blackbeard. The problem was, the story was set in 1820, and anyone who knows anything about pirates knew that by then Blackbeard had been dead for a century. It was one of those things so jarring that it was impossible to take her seriously. She was surprised when I mentioned that was a really bad mistake. What did it matter? In this case, it made it impossible to go another step in the story. She was flaunting the fact that she didn't know her subject. (The writing was also really bad, so no loss to the world of pirate literature.)
There's a difference between not knowing something is wrong – Tori just coined the phrase "Anachronistic Amnesia," where you can't remember if something is from the right time period – and not caring. Not caring means you aren't thinking about the reader, and they get sensitive, they don't like that. You have to be alert to it, and it's not that hard to check.
I've written three pirate adventures, Chance, Chrissie Warren: Pirate Hunter, and now, Scurvy Dogs. I have to be sensitive to word choice. For instance, I have had to guard against anyone ever saying they were OK, or okay, because it didn't show up in the language until 1839, according ot the Online Etymology Dictionary, a very handy source for writers of historical fiction.
Tori, who is reading the final draft of Scurvy Dogs! while visiting our daughter and son in New York this week, caught me in two more that I never even thought about.
I have the agitated cook peeling potatoes, "really hacking away at those spuds." Turns out the word spud goes back to the 15th century, but at that time it only to describe a kind of knife. It wasn't applied to potatoes until 1845, in New Zealand. Now I could argue that modern readers would know what I meant and that's what matters, but if the story is told in the first person in 1701, there's no way the character could have used it. So it's out.
I also have the character, 14-year-old Jamie, say that if he ever ran into the Roman poet Virgil, "I'd smack him." How could that possibly be wrong? It's onomatopoeia, right? Except it's not. The word existed as early as the 1500s, but it only described a type of boat. Surprisingly, it didn't mean "hit with the hand" until the mid 19th century.
Would either of those hurt the story? Almost certainly not. But why take the chance? I can find ways around both of those. The last thing I want is some know-it-all clucking his tongue at me, deciding I don't know what I'm talking about, and tossing the book aside.
You want your reader to follow the story eagerly, willingly. You want it to flow, carrying the reader with you. Every
time you do something that might slow the reader, if even for a moment,
just a hiccup, you're creating unnecessary roadblocks. If you interrupt the flow too many times, the reader may decide not to get back in.