brat

Concise Oxford English Dictionary © 2008 Oxford University Press:
brat/brat/

▶noun derogatory or humorous a badly behaved child.

– derivatives
brattish adjective,
brattishness noun,
bratty adjective.

– origin C16: perh. an abbrev. of synonymous Scots bratchet, from OFr. brachet ‘hound, bitch’.