Here's why:
* Abstract nouns refer to concepts, qualities, or ideas that cannot be touched or seen. Examples include love, happiness, freedom, or justice.
* Concrete nouns refer to things that can be touched or seen. They have a physical existence.
"Assassination" refers to the act of killing someone, usually a politically important person, in a planned and often violent way. This act is a tangible event with specific details and consequences.
While the concept of "assassination" can be considered abstract, the word itself refers to a concrete action.