overrun vs run over

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

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

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

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

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

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