'Rucksack' is German for 'back-bag' — borrowed through Alpine mountaineering in the 1860s.
A bag with shoulder straps that allow it to be carried on the back; a backpack.
From German 'Rucksack,' a compound of 'Rücken' (back) and 'Sack' (bag, sack). The word entered English through the context of Alpine mountaineering, which was pioneered by British climbers in the Swiss and Austrian Alps during the mid-nineteenth century. The German/Swiss-German equipment vocabulary — 'Rucksack,' 'Eispickel' (ice axe), 'Bergschrund' (crevasse) — was
English 'ridge' and German 'Rücken' (back) are cognates — both from Proto-Germanic *hrugjō (back, spine). A mountain ridge is literally a mountain's 'back.' And the 'ruck' in 'rucksack' is a dialectal contraction of 'Rücken,' so a rucksack is literally a 'back-sack,' just as a backpack is a 'back-pack' — the two words are exact semantic parallels in different languages