Real Dictionary

lumber
uncountable noun: Lumber consists of trees and large pieces of wood that have been roughly cut up.
verb: If someone or something lumbers from one place to another, they move there very slowly and clumsily.

lumber in American English 1
miscellaneous discarded household articles, furniture, etc. stored away or taking up room
to fill or obstruct with useless articles or rubbish; clutter
intransitive verb: to cut timber and prepare it for market
noun: timber sawed or split into planks, boards, etc
transitive verb: to convert (a specified amount, area, etc.) into lumber

lumber in American English 2
to move heavily, clumsily, and, often, noisily
intransitive verb: to move clumsily or heavily, esp. from great or ponderous bulk

lumber in British English 1
noun: logs; sawn timber
verb: to pile together in a disorderly manner

lumber in British English 2
to move awkwardly