brat /bræt/ BrE AmE noun [countable] informal
[ Date: 1500-1600 ; Origin: Perhaps from brat 'rough or torn piece of clothing' (10-20 centuries) , from Old Irish bratt 'cloak' ]
1 . a badly behaved child:
a spoiled brat
2 . army/navy/military etc brat American English a child whose family moves often, because one or both parents work for the army, navy etc
—bratty adjective