the world > action or operation > difficulty > types of difficulty > [noun] > quality of being difficult or exacting > a difficult or demanding task (5)
figurative. colloquial. An action or task requiring the prolonged exertion of effort, a struggle; a challenge. Cf. pull, n.1 6e.
In weakened use: a difficult or demanding task, esp. one seen as a test of one's abilities or character.
A particularly challenging situation, problem, etc.