Subtle Knife 

The Subtle Knife is a book written by Phillip Pullman and is the second installment in the series his Dark Materials.
In the series the Subtle Knife is a knife used to cut "windows" or "doors" to other worlds
the Subtle Knife is also known by the Greek name Æsahættr which translates into English as "God Destroyer" or Teleutaia makhaira which translates to "the last knife"
No known material was able to resist the knife, although it was breakable, should the wielder attempt to use it whilst thinking about a person they loved. It was the belief of certain individuals that this was because the knife was incapable of cutting through love.

He used the Subtle Knife to cut through worlds.

Subtle Knife by PiecesOfApril November 17, 2020

subtle knife 

the subtle knife is used to cut the cheese. cutting the cheese is to crack one off.

'i bet he's looking for the subtle knife'
=
'i bet he's gone for a wank'

subtle knife by Blacknose January 10, 2005