cut down vs lumber

cut down is not a noun while lumber is a noun.

Word	Noun	Adjective	Verb	Adverb
cut down	No	No	Yes	No
lumber	Yes	No	Yes	No

As verbs, lumber is a hyponym of cut down; that is, lumber is a word with a more specific, narrower meaning than cut down:

Other hyponyms of cut down include chop down, poleax, poleaxe, log, cut.

cut down (noun)	lumber (noun)
	an implement used in baseball by the batter
	the wood of trees cut and prepared for use as building material

cut down (verb)	lumber (verb)
cut down on; make a reduction in	cut lumber, as in woods and forests
intercept (a player)	move heavily or clumsily
cause to come or go down
cut with a blade or mower
cause to fall by or as if by delivering a blow
cut with sweeping strokes; as with an ax or machete