English dictionary

Hi there! I would be very grateful if anyone can help me with my search. I am looking for a specific english dictionary...it is made as a computer program where you fill in a certain word and it gives you the meaning of the word and a list of many other word related to it. For instance you type in the word 'doctor' and it gives you definition and other word like nurse,hospital,treatment etc.
I had this program on my computer long time ago, but I've lost it and I can't find it now. It is very useful so if so.eone has any idea I will be very very grateful.
Best regards!