climb vs climb down

climb is a noun but climb down is not a noun.

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

climb (noun)	climb down (noun)
the act of climbing something
an event that involves rising to a higher point (as in altitude or temperature or intensity etc.)
an upward slope or grade (as in a road)

climb (verb)	climb down (verb)
go up or advance	come down
increase in value or to a higher point
improve one's social status
go upward with gradual or continuous progress
move with effort, by grasping
slope upward