Real Dictionary

clump
countable noun: A clump of things such as trees or plants is a small group of them growing together.
countable noun: A clump of things such as wires or hair is a group of them collected together in one place.
verb: If someone clumps somewhere, they walk there with heavy, clumsy steps.
verb: If things clump together, they gather together and form small groups or lumps.

clump in American English
a lump; mass
to plant in a clump; group together in a cluster
to walk heavily; tramp
intransitive verb: to walk heavily and clumsily
noun: a small, close group or cluster, esp. of trees or other plants
transitive verb: to gather or form into a clump; mass

clump in British English
noun: a cluster, as of trees or plants
verb: to walk or tread heavily