drop vs come down

drop is a noun but come down is not a noun.

Word	Noun	Adjective	Verb	Adverb
drop	Yes	No	Yes	No
come down	No	No	Yes	No

As verbs, come down is a hypernym of drop; that is, come down is a word with a broader meaning than drop:

Other hypernyms of drop include descend, fall, go down.

drop (noun)	come down (noun)
the act of dropping something
a central depository where things can be left or picked up
a curtain that can be lowered and raised onto a stage from the flies; often used as background scenery
a sudden sharp decrease in some quantity
a free and rapid descent by the force of gravity
a predetermined hiding place for the deposit and distribution of illicit goods (such as drugs or stolen property)
a steep high face of rock
a small indefinite quantity (especially of a liquid)
a shape that is spherical and small

drop (verb)	come down (verb)
give birth; used for animals	get sick
grow progressively worse	be the essential element
go down in value	criticize or reprimand harshly
stop pursuing or acting	move downward and lower, but not necessarily all the way
change from one level to another	fall from clouds
lower the pitch of (musical notes)
fall or sink into a state of exhaustion or death
leave undone or leave out
omit (a letter or syllable) in speaking or writing
utter with seeming casualness
lose (a game)
take (a drug, especially LSD), by mouth
remove (cargo, people, etc.) from and leave
to remove
cause to fall by or as if by delivering a blow
let or cause to fall in drops
to fall vertically
let fall to the ground
fall or descend to a lower place or level
pay out
stop associating with
terminate an association with
hang loosely