lumber vs timber

lumber and timber both are nouns.

Word	Noun	Adjective	Verb	Adverb
lumber	Yes	No	Yes	No
timber	Yes	No	No	No

As nouns, lumber and timber are synonyms defined as:

lumber and timber: the wood of trees cut and prepared for use as building material

lumber (noun)	timber (noun)
an implement used in baseball by the batter	a beam made of wood
the wood of trees cut and prepared for use as building material	a post made of wood
	(music) the distinctive property of a complex sound (a voice or noise or musical sound)
	land that is covered with trees and shrubs
	the wood of trees cut and prepared for use as building material

lumber (verb)	timber (verb)
cut lumber, as in woods and forests
move heavily or clumsily