paper knives

The terms paper knife and letter opener are often used interchangeably to refer to a knife-like desktop tool. In truth, they are actually for different functions and were in use at different times. Paper knives are used for cutting open the pages of hand-produced books where the folding of printed sheets creates some closed edges that require severing of the paper before reading. (This is in quarto and smaller formats where sheets are folded twice or more.) (https://en.wikipedia.org/wiki/Paper_knife, accessed 12 Mar 2021)