international organization vs international organisation

international organization and international organisation both are nouns.

Word	Noun	Adjective	Verb	Adverb
international organization	Yes	No	No	No
international organisation	Yes	No	No	No

As nouns, international organization and international organisation are synonyms defined as:

international organization and international organisation: an international alliance involving many different countries

Other synonyms of international organization include global organization, world organisation, world organization.

international organization (noun)	international organisation (noun)
an international alliance involving many different countries	an international alliance involving many different countries