Merriam-Webster, “terrorism”:

Definition of TERRORISM

• : the systematic use of terror especially as a means of coercion

 

Merriam-Webster, “terror”:

Definition of TERROR

1. : a state of intense fear
2. 1. : one that inspires fear : scourge
   2. : a frightening aspect <the terrors of invasion>
   3. : a cause of anxiety : worry
   4. : an appalling person or thing; especially : brat
3. : reign of terror
4. : violent or destructive acts (as bombing) committed by groups in order to intimidate a population or government into granting their demands <insurrection and revolutionary terror>

 

In recent years public tend to perceive “terror” as #4. Nonetheless, this word has other valid meanings, and #1 and #2 precisely describe trolls’ methods.