chop vs chop down

chop is a noun but chop down is not a noun.

Word	Noun	Adjective	Verb	Adverb
chop	Yes	No	Yes	No
chop down	No	No	Yes	No

chop (noun)	chop down (noun)
a tennis return made with a downward motion that puts backspin on the ball
a grounder that bounces high in the air
a jaw
a small cut of meat including part of a rib
the irregular motion of waves (usually caused by wind blowing in a direction opposite to the tide)

chop (verb)	chop down (verb)
hit sharply	cut down
cut with a hacking tool
cut into pieces with repeated blows
strike sharply, as in some sports
form or shape by chopping
move suddenly