Sisyphean
Concise Oxford English Dictionary © 2008 Oxford University Press:
Sisyphean /ˌsɪsɪˈfiːən/
▶adjective denoting a task that can never be completed.
– origin C16: from Sisyphus in Greek mythology, who was condemned to the eternal task of rolling a large stone to the top of a hill, from which it always rolled down again.
'Sisyphean' also found in these Oxford entries:
