What are the different meanings of the word "radical" in its adjectival form? [closed]

The etymology of radical is of or having roots.

As the OP has quoted, the Oxford dictionary says that it is "based on thorough or complete political or social reform" and "representing or supporting an extreme section of a political party."

The unnamed Muslim scholar is a radical if he supports going back to the roots of Islam. (I won't veer into whether he is of the Sunni or Shia branch; that is quite another story.) He might be seen as radical if those roots include some of the more extreme aspects, such as executing infidels.

He would not be considered a radical if he were to promote either the milder or more recent developments among Muslims. (An example of the former would be giving alms. Even though this is one of the pillars of Islam (and thus a root), he would not be considered radical if he were to promote alms-giving.)

There is some sense in which radical is in the eye of the beholder. The western press considers execution of a journalist as extreme and deplorable, but the giving of alms as mild and commendable.