Prostitution and the Constitution

I'm not too good with words but I've been taught to understand that pros are good and cons are bad. Just like pros is short for professionals that make a lot of money and get the chicks while cons is short for convicts or con artists that try to steal money but go to jail instead and don't get the chicks (instead, other dudes get them). So then whats the deal with the words prostitution and constitution? Prostitution begins with PRO but is apparently looked down upon and constitution begins with CON but is seemingly a positive approach to government. But is it really? Maybe these words are most appropriate as they are.