Latin from probatum which means a thing proved.
In use in the common law since at least 1463 (Bury Wills, Camden), referring to the proving of a will and the formal vesting of estate administration authority in an executor.
In England, by virtue of the Probate Act of 1857, the proving of wills was taken from the ecclesiastical courts and given to the regular or common courts.
Today, the word refers to both the application process and formal certificate or order given by a court that certifies that a will has been proven, validated and registered and which, from that point on, gives the executor the legal authority to execute the will.
A "probate court" is a name given to the court that has this power to ratify wills.