Mortar (masonry)
From Memory Alpha, the free Star Trek reference
Mortar was a substance used in masonry to bind construction blocks (such as those made out of stone) together and fill the gaps between them.
In 2373, Captain Sisko marveled at a painting containing a Bantaca spire, noting that the structure was made of hundreds of stones carved and fitted together so tightly that they didn't require mortar. (DS9: "Rapture")
