IPA: /ˈtrɪɡərˌmæn/
KK: /ˈtrɪgərˌmæn/
A person who uses a gun to shoot someone, often in a planned or criminal way, especially in gang-related activities.
The police arrested the triggerman involved in the recent shooting.
Triggerman is formed from "trigger" (from Middle English *triggen*, meaning to pull or activate) and "man" (from Old English *mann*, meaning a person). The word refers to a person who pulls the trigger of a firearm, typically in a criminal context.
Think of someone who 'activates' ('trigger') a weapon, and the 'man' just means a person. This helps you remember that a triggerman is someone who pulls the trigger.