What it means
The ending of names for cutting tools. A dermatome is an instrument that cuts thin slices of skin for grafts (the same word also names the strip of skin supplied by one spinal nerve), and an osteotome is a chisel for cutting bone. It is related to -tomy, which means the act of cutting, as in a tracheotomy.
Remember it
-tome is the tool; -tomy is the cut it makes.