reckless; rash; irresponsible

He had a harum-scarum youth.

disorganized; uncontrolled.

recklessly; wildly

He ran harum-scarum all over the place.

a reckless person.

reckless or unpredictable behavior or action.

adjective

carefree , careless , daring , disorderly , erratic , flighty , foolhardy , giddy , haphazard , hasty , imprudent , irresponsible , light-minded , negligent , rash , regardless , romping , scatty , thoughtless , wild , brash , headlong , hotheaded , ill-considered , impetuous , improvident , impulsive , incautious , madcap , precipitant , precipitate , reckless , slapdash , temerarious , unconsidered , (colloq.) wild , foolish , hare-brained , harebrained , indiscreet , volatile