run over vs overrun

run over is not a noun while overrun is a noun.

Word	Noun	Adjective	Verb	Adverb
run over	No	No	Yes	No
overrun	Yes	No	Yes	No

As verbs, run over and overrun are synonyms defined as:

Other synonyms of run over include brim over, overflow, well over.

run over (noun)	overrun (noun)
	too much production or more than expected

run over (verb)	overrun (verb)
injure or kill by knocking (someone or something) down and passing over the body, as with a vehicle	run beyond or past
flow or run over (a limit or brim)	seize the position of and defeat
	flow or run over (a limit or brim)
	invade in great numbers
	occupy in large numbers or live on a host