whetstone - a flat stone for sharpening edged tools or knives

sharpen - make sharp or sharper; "sharpen the knives"

set - give a fine, sharp edge to a knife or razor

optimise, optimize - make optimal; get the most out of; use best; "optimize your resources"

ameliorate, improve, meliorate, amend, better - to make better; "The editor improved the manuscript with his changes"

polish up, brush up, round off, polish, round - bring to a highly developed, finished, or refined state; "polish your social manners"