undercut vs cut down

undercut is a noun but cut down is not a noun.

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

undercut (noun)	cut down (noun)
(sports) a stroke that puts reverse spin on the ball
a cut made underneath to remove material
a notch cut in the trunk of tree in order to determine the direction of its fall
the tender meat of the loin muscle on each side of the vertebral column
the material removed by a cut made underneath

undercut (verb)	cut down (verb)
strike (the ball) in golf, tennis, or hockey obliquely downward so as to give a backspin or elevation to the shot	cut down on; make a reduction in
cut away the underpart of	intercept (a player)
cut away material from the underside of (an object) so as to leave an overhanging portion in relief	cause to come or go down
cut obliquely into (a tree) below the main cut and on the side toward which the tree will fall	cut with a blade or mower
sell cheaper than one's competition	cause to fall by or as if by delivering a blow
	cut with sweeping strokes; as with an ax or machete