Slice off the "flower" end leaving the "root" end intact. Cut the onion in half on longitude. Working with your knife against the plane starting from the part you've just cut off, slice sideways almost to the root which is still holding the thing in place---making one or more slices depending on size of onion. Working from the top side, the curve of the earth, apply several more cuts heading away from the root (are you still with me?). Now slice across from cut end down and you will have a dice.