up ‧ start /ˈʌpstɑːt $ -ɑːrt/ BrE AmE noun [countable]
[ Date: 1500-1600 ; Origin: upstart 'to jump up suddenly' (14-19 centuries) ]
someone who behaves as if they were more important than they really are and who shows a lack of respect towards people who are more experienced or older:
a cheeky young upstart
—upstart adjective