Final answer:
A handwritten, signed but unwitnessed testamentary document is called a holographic will. It is entirely in the testator's handwriting and can be valid even without witnesses in some jurisdictions.
Step-by-step explanation:
A handwritten, signed, but unwitnessed testamentary document would be referred to as a holographic will. This type of will is written entirely in the handwriting of the testator (the person making the will) and does not necessarily need to be witnessed to be considered valid, though this can vary by jurisdiction. Despite its potential for easy challenge in court due to lack of formal witnessing, a holographic will can be a legally binding document if it meets the specific state requirements where it is presented.
The term manuscript originates from the Latin words manus (hand) and scriptus (written), which describes a document written by hand. Just like a manuscript can be an intricately decorated handwritten document, a holographic will is a testamentary letter of intent that is informal and handwritten by an individual looking to detail how their assets should be distributed after their death.