The act or fact of establishing something together with someone else, or institutions that are jointly founded.
From co- (together) + establishment (from Old French establir, from Latin stabilire meaning 'to make firm or stable') + -ment (noun suffix). The co- prefix was added in English to indicate joint or mutual establishment.
This word appears in historical documents when two powers or groups created something together—like when the United States and Britain coestablished research institutions after World War II.
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