A difficulty that has to be resolved or dealt with.
A puzzling circumstance.
A set of moves required to complete a climb.
A question to be answered, schoolwork exercise.
Objection.
Difficulty in accepting or understanding or refusal to accept or understand.
Causing a problem; problematic; troublesome.
Difficult to train or guide; unruly.
Something troublesome or difficult to handle.
A hardy, resilient animal or plant.
A person who can endure physical or mental hardship; a hardened, strong-willed person.