fall upon vs strike

fall upon is not a noun while strike is a noun.

Word	Noun	Adjective	Verb	Adverb
fall upon	No	No	Yes	No
strike	Yes	No	Yes	No

As verbs, fall upon and strike are synonyms defined as:

Other synonyms of fall upon include attain, chance on, chance upon, come across, come upon, discover, happen upon, light upon.

fall upon (noun)	strike (noun)
	a group's refusal to work in protest against low pay or bad work conditions
	a score in tenpins: knocking down all ten with the first ball
	an attack that is intended to seize or inflict damage on or destroy an objective
	a conspicuous success
	(baseball) a pitch that the batter swings at and misses, or that the batter hits into foul territory, or that the batter does not swing at but the umpire judges to be in the area over home plate and between the batter's knees and shoulders
	a gentle blow

fall upon (verb)	strike (verb)
find unexpectedly	cause to form (an electric arc) between electrodes of an arc lamp
	arrive at after reckoning, deliberating, and weighing
	indicate (a certain time) by striking
	make a strategic, offensive, assault against an enemy, opponent, or a target
	deliver a sharp blow, as with the hand, fist, or weapon
	hit against; come into sudden contact with
	affect or afflict suddenly, usually adversely
	produce by manipulating keys or strings of musical instruments
	remove by erasing or crossing out or as if by drawing a line
	pierce with force
	smooth with a strickle
	hook by a pull on the line
	produce by ignition or a blow
	form by stamping, punching, or printing
	disassemble a temporary structure, such as a tent or a theatrical set
	have an emotional or cognitive impact upon
	drive something violently into a location
	occupy or take on
	cause to experience suddenly
	find unexpectedly
	stop work in order to press demands
	attain
	touch or seem as if touching visually or audibly