Geology: A → sedimentary particle that is larger than 256 mm in size. Boulders are the largest particles of sediment that occur in streams and can reach the size of a small house (geology.com/dictionary).
From late M.E. bulder, possibly from Swedish bullersten "noisy stone" (large stone in a stream, causing water to roar around it), from buller "noisy" + sten "stone."
Gordâle "boulder" (used in various areas of Iran: Šuštar, Kermânšâh, Nahâvand, Ali-Gudarz), from gord "kidney" + similarity/relation suffix -âl, → -al.