Dongsaeng is a
Korean word describing a family or friendship
relationship. It is used to refer to one's younger
sibling or a close friend that is younger than oneself.
"I promised my dongsaeng I'll treat her for dinner if she did
well on her
test."
"Dongsaeng, make me a cup of coffee."
(Although the above statement is a command, 'dongsaeng' acts as a form of endearment like 'little
brother' or 'little sister'. In other words: "Lil' bro, how about a cup of coffee for your big bro?")