frat·er·nize fraternizes fraternizing fraternized in BRIT, also use fraternise If you fraternize with someone, you associate with them in a friendly way. At these conventions, executives fraternized with the key personnel of other banks Mrs Zuckerman does not fraternize widely The recession has created an atmosphere where disparate groups fraternise in an atmosphere of mutual support. = mix. to be friendly with someone, especially if you have been ordered not to be friendly with them fraternize with