international organisation vs international organization

international organisation and international organization both are nouns.

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

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

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

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

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