Went straight to CoC. Picked up "black long sword", I think it was in the big room.

I haven't played ADOM much for a few years so I'm a bit rusty. I figured it was like when you find a yellow or white weapon, and there was no surge of power. So I continue to Dwarftown thinking I would identify it soon...

Killed by mimic in Dwarftown shop (I was chaotic so couldn't lure it to altar).

Examine inventory: Kinslayer.
Look it up on the wiki: best one-handed sword in the game.