A tool is defined as a weapon-tool if it has a weapon skill.
Weapon-tools in vanilla NetHack are:
|unicorn horn||unicorn horn||yes||bone|
Note that the dwarvish mattock, despite being usable in exactly the same way as a pick-axe and using the same weapon skill, is actually classified as a weapon. Also, axes and battle-axes can be applied to break down doors, but are not tools.