An Etymological Dictionary of Astronomy and Astrophysics

1. An instrument for cutting, consisting essentially of a thin, sharp-edged, metal blade fitted with a handle.
   

2. Any blade for cutting, as in a tool or machine (Dictionary.com).

Etymology (EN): M.E. knif; O.E. cnif, probably from O.N. knifr;
cf. M.L.G. knif, M.Du. cnijf, Ger. Kneif; of uncertain origin.

Etymology (PE): Kârd “knife,” from Mid.Pers. kârt “knife;” Av. karət- “to cut;” cf. Skt. kart- “to cut,”
karəta- “knife;” Proto-Ir. *kart- “to cut.”