Word that fits this definition a weapon of execution?

There isn't one single perfect word that fits the definition of "a weapon of execution" because the term encompasses various tools and methods.

Here are some options, depending on the specific context:

General terms:

* Executioner's tool

* Instrument of death

* Capital punishment device

Specific terms:

* Guillotine

* Electric chair

* Hangman's noose

* Firing squad

* Lethal injection

The best word depends on the specific context and the desired level of detail.