From Old Norse 'knifr,' replacing native 'seax' — the very word the Saxons took their name from.
A cutting instrument consisting of a sharp blade attached to a handle, used for slicing, piercing, or as a weapon.
From Old English 'cnīf,' borrowed from Old Norse 'knífr,' from Proto-Germanic *knībaz, of uncertain deeper origin — possibly from a pre-Germanic substrate language or from a PIE root meaning 'to pinch' or 'to compress.' The initial 'kn-' cluster was pronounced in Old and Middle English but fell silent by the seventeenth century. The word replaced the native Old English 'seax,' which had been the standard Germanic word for a short blade. Key roots: *knībaz (Proto-Germanic: "knife, short blade").
English once had a native word for knife: 'seax,' which was so central to Anglo-Saxon identity that the Saxons literally named themselves after it — 'Saxon' comes from 'seax.' The Old Norse 'knífr' displaced it during the Viking Age, so the English word for knife is actually a Viking import.