Boulder

Boulder \BOHL-der\ , noun;
1. A detached and rounded or worn rock, especially a large one

This word dates to 1607 as a shortening of boulder-stone, which derives from Middle English bulderston. The exact etymology of the English words are uncertain, but there is a word in Swedish bullersten, which is a large stone in a stream as opposed to klappersten, a small pebble. Bullersten is a combination of buller + sten ("noise" + "stone"). Bulderston probably derives from the same source as bullersten, but since there are no similar words in other Germanic languages it is hard to establish a firm link between the two. Plenty of Germanic languages have cognates with the first element, bulder-, but no one except us and the Swedes compound it with something like -stone.