fall vs decline

fall and decline both are nouns.

Word	Noun	Adjective	Verb	Adverb
fall	Yes	No	Yes	No
decline	Yes	No	Yes	No

As nouns, fall and decline are synonyms defined as:

Other synonyms of fall include declension, declination, declivity, descent, downslope.

As verbs, decline is a hyponym of fall; that is, decline is a word with a more specific, narrower meaning than fall:

As verbs, decline is a hyponym of fall; that is, decline is a word with a more specific, narrower meaning than fall:

fall (noun)	decline (noun)
a sudden drop from an upright position	a downward slope or bend
the act of surrendering (usually under agreed conditions)	a gradual decrease; as of stored charge or current
a lapse into sin; a loss of innocence or of chastity	change toward something smaller or lower
a sudden sharp decrease in some quantity	a condition inferior to an earlier condition; a gradual falling off from a better state; decline
a free and rapid descent by the force of gravity
a sudden decline in strength or number or importance
when a wrestler's shoulders are forced to the mat
a movement downward
a downward slope or bend
the season when the leaves fall from the trees
the time of day immediately following sunset

fall (verb)	decline (verb)
occur at a specified time or place	grow smaller
decrease in size, extent, or range	grow worse
pass suddenly and passively into a state of body or mind	show unwillingness towards
be born, used chiefly of lambs	inflect for number, gender, case, etc.
come out; issue	go down
assume a disappointed or sad expression	fall in value
begin vigorously	not accept as true
come as if by falling
be cast down
go as if by falling
fall or flow in a certain way
move downward and lower, but not necessarily all the way
move in a specified direction
descend in free fall under the influence of gravity
slope downward
drop oneself to a lower or less erect position
lose an upright position suddenly
to be given by assignment or distribution
be captured
fall to somebody by assignment or lot; passed
come into the possession of
to be given by right or inheritance
be inherited by
lose office or power
yield to temptation or sin
suffer defeat, failure, or ruin
lose one's chastity
die, as in battle or in a hunt
be due
come under, be classified or included
touch or seem as if touching visually or audibly
fall from clouds