What is Anticipation?

Legal Definition
Anticipation, or being enthusiastic, is an emotion involving pleasure, excitement, and sometimes anxiety in considering some expected or longed-for good event.
-- Wikipedia
Legal Definition
In patent law, anticipation refers to the prior invention or disclosure of the claimed invention by another, or the inventor's own disclosure of the claimed invention by publication, sale, or offer to sell prior to the inventor's application for a patent. In other words, if someone else has known about or used the invention before the patent applicant applies for a patent, that patent applicant will not be entitled to a patent.

Anticipation is a grounds for invalidating or rejecting a patent because it means that the claimed invention lacks novelty. Patent invalidity based on lack of novelty, or anticipation, requires that the invention was known or used by others before it was invented by the patentee.
Legal Definition
The act of doing or taking a thing before its proper time.

2. In deeds of trust there is frequently a provision that the income of the estate shall be paid by the trustee as it shall accrue, and not by way of anticipation. A payment made contrary to such provision would not be considered as a discharge of the trustee.
-- Bouviers Law Dictionary
Legal Definition
The act of doing or taking a thing before its proper time. In conveyancing, anticipation is the act of assigning, charging, or otherwise dealing with income before it becomes due. In patent law, a person Is said to have been anticipated when he patents a contrivance already known within the limits of the country granting the patent. Topliff v. Topliff, 145 U. S. 156, 12 Sup. Ct. 825, 36 In Ed. 658; Detroit, etc., Co. v. Renchard (C. Ct) 9 Fed. 298; National Hollow Brake Beam Co. v. Interchangeable Brake Beam Co. (C. C.) 99 Fed. 772.
-- Black's Law Dictionary
Legal Definition
The premature doing of an act.
-- Ballentine's Law Dictionary