Definitions of sharpen:

• verb:   make (images or sounds) sharp or sharper
• verb:   become sharp or sharper

  Example: "The debate sharpened"

• verb:   make sharp or sharper

  Example: "We had to sharpen our arguments"

• verb:   make (one's senses) more acute

  Example: "This drug will sharpen your vision"

• verb:   give a point to
• verb:   raise the pitch of (musical notes)
• verb:   make sharp or sharper

  Example: "Sharpen the knives"

• verb:   put (an image) into focus