Origins
Every trigger is a pull. The word comes from Dutch trekker, meaning 'puller', from trekken — 'to pull, to draw'. The Dutch were Europe's leading firearms manufacturers in the 16th and 17th centuries, and English gunmakers imported their vocabulary along with their weapons.
The mechanics are preserved in the word. A trigger is a lever that you pull. It releases a catch, which releases a spring, which strikes a charge. The action is simple — a single pull — but the consequences are irreversible. This mechanical clarity is why trigger became the default metaphor for causation.
The 20th century extended the word far beyond guns. A trigger event starts a chain reaction. A trigger warning signals distressing content ahead. An emotional trigger activates a psychological response. In every case, the metaphor is the same: one small pull, one large consequence.
Later History
Dutch trekken produced another English word by a different route. In South Africa, Afrikaans-speaking Boer settlers used trek to describe their ox-wagon migrations — journeys where animals pulled heavy loads across vast distances. The Great Trek of the 1830s gave English the word for any long, arduous journey.
Star Trek borrowed the word for a voyage beyond the frontier. A trigger and a trek share the same root: both begin with a pull. One is instantaneous, the other endless.