What is "to deal in futures"

Future \Fu"ture\, n. [Cf. F. futur. See Future, a.]

1. Time to come; time subsequent to the present (as, the future shall be as the present); collectively, events that are to happen in time to come. ``Lay the future open.''
   --Shak.

2. The possibilities of the future; -- used especially of prospective success or advancement; as, he had great future before him.

3. (Gram.) A future tense.

   To deal in futures, to speculate on the future values of merchandise or stocks. [Brokers' cant]