You may have asked yourself what that means. It's pretty simple and if you don't know, grab a dictionary. But I'll save you the trouble.
1. Stiffly or artificially formal; stiff.
2. Architecture Having some vertical length between the impost and the beginning of the curve. Used of an arch.
So now you know the definition. What does that mean to you? If you are getting comments on your stilted dialogue, it means it just doesn't sound believable. Dialogue should flow. It should sound like real speech but with all the boring parts taken out. No one wants to read every comment of every conversation. It should be normal conversation but better.
Take for instance:
Person 1: Do you have any milk? I had to dump my last cup when I added the wrong thing from my recipe to it.
Person 2: No, sorry, but hey, what's the number to your plumber?
P1: Oh, hang on a sec, I'll get it for you. Um, yeah. Wait, I know where it is. I think it's somewhere in my junk drawer.
P2: You know, if you just know the name, I'll google him.
P1: Tsk, oh, um, I can't remember. It's something like, um--
P2: Wait, wasn't it something like, um, Crane something or other?
P1: Yeah, I, uh, think so. I'm pretty sure it was something like that.
I could go on with useless drivel that we all do but I think it's unnecessary. This is an example of normal, every day conversation that we all do. Okay, so maybe not exactly like this but close enough. But it's boring to read. The only important thing in here for someone reading would be the question and the answer. Do you have any milk? No, sorry I don't. Just ran out. All the other boring stuff is taken out.
Here's the same language in stilted dialogue:
P1: Would you happen to have any milk in your refrigerator? I ruined my last cup when I added the wrong spice and now my carton is empty.
P2: No, I'm afraid I have no milk. But whilst your here, would you mind, what is the name of your plumbing specialist?
P1: Let me excogitate on that for a moment. I believe it referenced a Crane of some sort.
P2: I believe you are correct. I recall the sign on the van said something similar to such.
Completely over the top, yes, I know. Note the thesaurus moment. These happen amazingly often. But this is language that is much too formal. People don't really talk like that.
So when you are writing your dialogue, read it out loud. Does it sound right? Does it sound like something a person would actually say? If you have characters that are not native to English (aliens and whatnot) try to keep it real. Yes, the language may be more formal but it would fit the character so long as you don't go digging around the thesaurus too much.
So many writers think that using big words somehow gives them credibility as a writer. It doesn't. People want to read. They want a good story. They want it to flow. They want to feel. They don't want to feel like the author is trying to prove some kind of superiority. Use big words if it makes sense and fits the character and the plot. But usually you can get away with just using a simple word that conveys a heck of a lot more than "I grabbed a thesaurus."
I realize this post was not very well planned. It's a bit all over the place. But I'm trying to do this while cooking dinner. Shoot me. Kids have to eat. :)