adjective exciting; great. Combining two clichés of 'swinging sixties London' (from a Hollywood perspective): SHAG (to have sex) and 'psychedelic' (of mind-expanding drugs). Usage has added sexual overtones to this comic coinage which appears just once in the film Austin Powers, The Spy Who Shagged Me: 'New case? Very shagadelic, Basil!' (Mike Myers, 1998) US, 1998