old-fashioned slang Crazy, insane, or mentally deranged. Sometimes written as "off (one's) 'nana" to reflect the abbreviation of "banana." I think you've gone off your nana for giving up that cushy office job, but, hey, follow your dreams. Don't go off your 'nana, I only took the car out for a quick spin. My auntie likes to let people think she's off her nana, but she's actually incredibly clever and witty.