clump 
(klŭmp)
(klŭmp)n.
1. A clustered mass; a lump: clumps of soil.
2. A thick grouping, as of trees or bushes.
3. A heavy dull sound; a thud.
v. clumped, clump·ing, clumps
v.intr.
1. To form lumps or thick groupings.
2. To walk or move so as to make a heavy dull sound.
v.tr.
To gather into or form lumps or thick groupings of.
[Probably Low German klump, from Middle Low German klumpe, cluster of trees.]
clumpy adj.