the name sanatan was given by Adi shankaracharya...and the name hindu was given by i think persians(i may be wrong i am not sure) because of those people who used to live around Sindhu or Indus river.
initially the word Dharm(religion) and karm(action) were synonyms of each other,and there were four kinds of action(karm)..to be associated with knowledge(brahaman)<remember at that time brahaman was a action and reward not cast>...to save and secure people(kshatriya),business(vaishya)...cleaning and serving the society(shoodra)....and shoodra was word not cast......but later brahaman becomes strong and they created such an environment which is still making differences and generates strong violence.think deep then reach to conclusion.