knock over vs overturn

knock over is not a noun while overturn is a noun.

Word	Noun	Adjective	Verb	Adverb
knock over	No	No	Yes	No
overturn	Yes	No	Yes	No

As verbs, knock over and overturn are synonyms defined as:

knock over and overturn: cause to overturn from an upright or normal position

Other synonyms of knock over include bowl over, tip over, tump over, turn over, upset.

knock over (noun)	overturn (noun)
	the act of upsetting something
	an improbable and unexpected victory

knock over (verb)	overturn (verb)
cause to overturn from an upright or normal position	change radically
	rule against
	cancel officially
	turn from an upright or normal position
	cause to overturn from an upright or normal position
	cause the downfall of; of rulers