IPA: /əˌsæsɪˈneɪʃən/
KK: /əˌsæs.ɪˈneɪ.ʃən/
The act of killing someone, usually a prominent person, for political or ideological reasons.
The assassination of the leader shocked the entire nation.
Assassination is formed from "assassin" (from Old French *assassiner*, meaning to murder) and the suffix "-ation" (meaning the action or process of). The word refers to the act or process of murdering someone, particularly for political reasons.
Think of the act of 'murdering' ('assassin') as a specific action ('-ation') — that's why assassination means the act of murder, especially for political motives.