Definition of paper knife in US English:

paper knife

noun

  • A blunt knife used for cutting paper, such as when opening envelopes or slitting the uncut pages of books.

    • ‘Calypso smiled and raised her eyes to heaven, then reached for a paperknife and slit open one of the envelopes.’
    • ‘Sometimes a paperknife is used but it may be difficult to insert the tip of the knife under the flap.’