Most native English speakers hate hearing the word rucksack. For some reason, it grates on their senses. Did you know that there’s more to this ugly noun than meets the ear? There’s a reason why the synonym for backpack is the way it is. First of all, English is a Germanic language. The German word for back, the body part your mom constantly complains about, is Ruecken. Der Ruecken is the back, for example. Do you see the connection? Rucksack. Ruecken. In addition, the German word Sack translates to bag in English.
In short: a rucksack is actually a backbag!
This has been Amateur Etymologist Fun on Real Eccentric!
Read more about the word rucksack here (interestingly enough, the word Bergen in German mean mountains in English.