The word commensurate has to do with things that are similar in size and therefore appropriate. Many people think the death penalty is a commensurate punishment for murder. In other words, the penalty fits the crime.
When things are commensurate, they're fair, appropriate, and the right size. If you got a ticket for jaywalking, you shouldn't get ten years in prison — that penalty is not commensurate with the crime. The word commensurate is usually followed by with or to; one thing is commensurate with or to another.