noun

a close friend.

she shared the cake with her chums

friend,companion,intimate,familiar,confidant,alter ego,second self,playmate,classmate,schoolmate,workmate,pal,buddy,bosom pal,sidekick,cully,spar,crony,main man,mate,oppo,china,mucker,butty,marrow,marra,marrer,amigo,compadre,paisan,bro,homeboy,gabba,compeer,fidus Achates

verb

form a friendship with someone.

his sister chummed up with Sally