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).

In all likelihood.

(surgery) Any of various medical instruments used to explore wounds, organs, etc. / (figuratively) Something which penetrates something else, as though to explore; something which obtains information.

(transitive, intransitive) To explore, investigate, or question / (transitive) To insert a probe into.

(statistics) A distribution of all possible values of a random variable together with an indication of their probabilities.

A model of Ford automobile.

(entomology, malacology) The tubular feeding and sucking organ of certain invertebrates like insects, worms and molluscs. / The trunk of an elephant.

Abbreviation of procedure. / Abbreviation of processor. / Abbreviation of programmed random occurrence.