A difficulty that has to be resolved or dealt with. / A question to be answered, schoolwork exercise. / A puzzling circumstance. / Objection.

(of a person or an animal) Difficult to train or guide; unruly. / Causing a problem; problematic; troublesome.

Integrity, especially of the quality of having strong moral principles; decency and honesty.

Likely or most likely to be true. / Likely to happen. / Supporting, or giving ground for, belief, but not demonstrating. / (obsolete) Capable of being proved.

Something that is likely. / A person who is likely to appear or do a certain thing.

The state of being probable; likelihood. / An event that is likely to occur. / The relative likelihood of an event happening.

(mathematics, UK, Canada) The problem in combinatorial optimization in which, given a number of cities and the costs of travelling from one to the other, it is required to determine the cheapest route that visits each city once and then returns to the initial city.

Difficult to overcome, solve, or decide. / Not settled, uncertain, of uncertain outcome; debatable, questionable, open to doubt.

(chiefly in the plural) A problem or difficulty in a particular field of study.

(mathematics) The mathematical study of probability (the likelihood of occurrence of random events in order to predict the behavior of defined systems).