“Semantically — in its most accurate meaning — political ‘“radicalism’” is a characteristic of the extreme political left, whereas ‘“reactionary’” is the more correct term for the extreme political right.”

No, that’s not what that means at all. Radicalism is extremist ideology of any caliber, or position.

From [Merriam-Webster’s Dictionary]: “A: very different from the usual or traditional; extreme; B: favoring extreme changes in existing views, habits, conditions, or institutions; C: associated with political views, practices, and policies of extreme change; D: advocating extreme measures to retain or restore a political state of affairs.”

The reason why “reactionary” got assigned to the right is because during the time period the you’re talking about, many governments and areas converted to socialism, or an extreme version of state-controlled government (think the eponymous “big government”). 

In states like China, those who opposed this “revolution” were described as “reactionaries” (to the revolution). Since the idea of the state was constructed from a far left (far, far, far, left), anyone who disagreed was right wing, relative to the state.

In short, reactionaries are those who oppose significant shifts. If you talk about reactionaries in Fascist Germany, you may talk about left-wing reactionaries. However, more recent examples have been reactions to socialist ideologies.

Radicals may exist without revolution. There’s always going to be people far, far outside the Overton window (the term for the acceptable “normal range” of local politics). 

Reactionaries are those who oppose revolution (and sometimes for good reason). They are not restricted at all by left, right, authoritarian, or libertarian. They are relative terms, so stop being so U.S.-centric.

“Ironically, the most frequent uses describe the ‘“radicalism’” of Islam or right-wingers.” You should honestly be thankful for that. 

The qualifier of “extreme” means that the speaker is acknowledging #NotAllMuslims, or #NotAllRepublicans (I take issue with the fact that you’ve grouped an entire subset of political ideologies into “right-wing,” but we can get to that later).

Editor’s Note: This comment has been edited for grammar and clarity.

User Rusty Shacklefort via mndaily.com