frac ‧ tious /ˈfrækʃəs/ BrE AmE adjective
[ Date: 1600-1700 ; Origin: fraction 'lack of agreement' (16-18 centuries) ]
someone who is fractious becomes angry very easily SYN irritable :
Children become fractious when they are tired.
fractious baby/child etc
—fractiousness noun [uncountable]