Random: Without System Or Order

The word comes from the German Rand which means rim, edge or outer limit. In the 16th Century, the word “random” came into English as a description for a man or horse running at the limits of its ability or for a gun that is fired at the maximum elevation to reach the outer limits of its range.

A gun fired in this manner sacrificed all accuracy to achieve that max range.  You would fire it and have no idea where the round would land. And that is where our everyday usage of the word comes from.