From Longman Dictionary of Contemporary Englishchummychum‧my /ˈtʃʌmi/ adjective FRIENDLY informal friendly You and Eric have become quite chummy, haven’t you?
Examples from the Corpus
chummy• I'd forgotten that Ellen and Gary had become chummy.• We shook hands, and she was about as chummy as a boxer before a fight.• Frost, though chummy enough, is like a prisoner in solitary confinement.• His tone toward Wyatt could be chummy one moment, businesslike the next, and sometimes, disconcertingly, both at once.• Diana was so chummy with him she even used to iron his shirts.• Sometimes the head man gets too chummy with the new boy and the old boys get jealous. 