The term 'keen quality' can be broken down into two crossword solutions: EDGE (4 letters) and BITE (4 letters). EDGE is a noun that refers to the sharpness of a blade or the thin line between two surfaces. BITE is a verb that means to cut into something with the teeth or to take hold of something firmly. Together, these two words describe a keen quality, which is a sharpness or intensity that is often associated with a skill or ability.