Synonyms for Harum-scarum (same or very similar meaning)
WordNet sense 1 (a reckless impetuous irresponsible person):
daredevil, hothead, lunatic, madcap, swashbucklerWordNet sense 2 (cheerfully irresponsible):
carefree, devil-may-care, freewheeling, happy-go-lucky, slaphappyWordNet sense 3 (showing lack of care for consequences):
irresponsibleWordNet sense 4 (in a wild or reckless manner):
pell-mellFrom the ODE community, based on WordNetadd/edit