Sharpening a knife is a process of making the blade sharper by removing metal from the EDGE. HONE, which is a four letter word, is the process of using a honing stone to sharpen the blade. WHET, another four letter word, is the process of using a whetstone to sharpen the blade. EDGE, the last four letter word, is the sharpened part of the blade. All three words, HONE, WHET, and EDGE, are related to the term sharpen as a knife.