וּשְׁעָרַיִךְ לְאַבְנֵי אֶקְדָּח
and provided the JPS translation:
"Your gates of precious stones (avnei ekdach)"
But if you're familiar with modern Hebrew, you would know that ekdach means "pistol, revolver". So what's the connection?
First, let's look at the biblical word, which only appears in this verse. The exact identity of the stone is not know, and so the JPS offers "precious stones." However, Targum Yonatan translates it as avnei gmar - and we have seen before that gmar means "coal" in Aramaic. Following the Targum, Rashi explains the word to be carbuncle, and that is offered by many other translations. Carbuncle is an obsolete word meaning "red precious stone", and gets its name from the "Latin carbunculus, small glowing ember, carbuncle, diminutive of carbō, carbōn-, coal". (Interestingly, carbuncle also means an infection of the skin, as does anthrax, which is also the Greek word meaning "coal".)
Klein says ekdach has a similar etymology to carbuncle:
Literally probably meaning 'flashing or sparkling stone' and derived from קדח (= to kindle). Compare Arabic qaddahah (= fire steel, fire iron).
The root קדח also means "to bore, to drill", and Klein feels that the meaning "to kindle" originally meant "to make fire by rubbing".
As far as ekdach meaning "revolver", this was a coinage of Ben Yehuda. In his dictionary, he says it means a weapon which shoots (fires) using firepower, which he derived from the root קדח - "to kindle, to burn". Based on this, Klein translates Ben-Yehuda's intention as "firearm".
However, lets look at the article where Ben Yehuda made his original suggestion (an article in his newspaper Hatzvi, 1896. The original can be viewed here, page 3.) He discusses there possible Hebrew words for "firearm" and rejects the term used at the time k'nei roveh קנה רובה, which Klein translates as "bowman's barrel". He says it sounds terrible in Hebrew, and would be difficult to make a plural of, conjugate, etc. David Yellin suggested shortening the word to roveh רובה, but Ben-Yehuda rejected that as well, for roveh should be the shooter, not the gun. (In the end, Modern Hebrew did adopt roveh for "rifle".)
Then he points out that many European languages have a word for a gun "in which a flint fixed in the hammer produces a spark that ignites the charge" - a flintlock in English. He therefore goes back to the stone ekdach, which based on Arabic, he connects to "flint". He points out that even if the actual stone referred to in Yeshayahu is identified, the word isn't commonly used, so there shouldn't be a problem appropriating the old word for a new meaning.
So if you like, when you hear the word ekdach, you can think of The Flintstones...