undercut vs strike down

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

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

undercut (noun)	strike 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)	strike down (verb)
strike (the ball) in golf, tennis, or hockey obliquely downward so as to give a backspin or elevation to the shot	cause to fall by or as if by delivering a blow
cut away the underpart of	cause to die, especially suddenly
cut away material from the underside of (an object) so as to leave an overhanging portion in relief	declare null and void; make ineffective
cut obliquely into (a tree) below the main cut and on the side toward which the tree will fall
sell cheaper than one's competition