Simply put, a will is a legal document intended to state how your property will pass upon your death.
It’s “revocable,” which means that you can revoke or change it anytime you want (until you lose your mind or die).
The phrase “last will and testament” exemplifies how legalese grows legs and then walks on for generations, no one remembering how or why or wherefore or heretofore or how in the hell the aforementioned got started – notwithstanding the foregoing.
Back in the merry old days after Arthur and Lancelot, closer to the time of Robin Hood, England’s justice system was split between the King’s courts and the church’s courts.
The King’s courts recognized the Old English word “will,” and the ecclesiastical courts recognized the Latin word “testament.”
To be on the safe side, a lawyer trying to develop a practice around used both.
Lexicological archaeologists don’t stop there.
Others contend that the early English were wild about redundancy, that “last will and testament” exemplifies this, as does “free and clear” and “had and received.”
I could go on, but I am starting to bore myself.