ἔμβολος

The ancient Greek embolos (ἔμβολος) meant a wedge, a plug, a peg, or a bolt — any object that is driven in to block or secure something. It named the bronze-sheathed ram on the prow of a warship that drove into an enemy hull; it named the pin of a door bolt; it named the wedge driven into a split log. The word derived from emballein — to throw in, thrust in — compounded from en- (in) and ballein (to throw), the same root that gives us ballistic, problem (something thrown before you), and symbol (thrown together). The notion of thrusting something into a channel and blocking it was built into the word from its earliest use.