bo I. variant of boo II. noun alsoboe\ˈbō\ (pluralboes) Etymology: by shortening slang: hobo III. noun (-s) Etymology: probably short for bozo or hobo slang: fellow, buddy — used chiefly in informal address < the truth is, bo, that the man's got a good name — Geoffrey Household > IV. noun (-s) Etymology: Singhalese bō — more at bo tree : pipal