[@Karl Kadaver] I Just had a thought reading your last post over again.....you used the phrase jumped the gun. "to start before the starting signal. (Originally used in sports contests that are started by firing a gun.)" And the more appropriate way you used it for, "to do something too soon, especially without thinking carefully about it"

It got me thinking. and I'm no way trying to say you did anything wrong, but as a writers thought. Can someone get away with saying Jumping the gun when there is no mention of the word 'guns' in this period...usually called cannons, or hand cannons (Or handgonnes). The earliest referring to 'Gun' was nordic for Gunilda which was an engine of war.  which was roughly the end of the 14th century. While the black plague ended roughly the same time. as we are just near this time, we are to close to the beginning of the use of the word "Gun" 

Now I know we have a musket wielder in the group. and we all think of this
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But that was mid 16th- 17th centuryish... as for our time, they were more like mini canons than guns we think of. So he is a bit early in his use of a musket, but i'm not picky on that as it is an alternate earth universe thing we are dealing with. 

But I digress. Can us as writers really use terminology for our life time in a setting before it was even conceived of or never existed? 

(Second example, Calling a room Spartan.... if you used a world where Spartan's (Greek soldiers from Sparta) doesn't exist?)

Can we still do this to help the reader understand what the character is feeling doing what ever? Or should we find an example of that time period that would fit closely enough that the reader could still get it?