IPA: /hɑːrˈpuːnər/
KK: /hɑrˈpunɚ/
A person who uses a long spear with a sharp point, called a harpoon, to catch large sea animals like whales.
The harpooner skillfully aimed his harpoon at the whale swimming nearby.
Harpooner → The word is formed from "harpoon" (from Middle French *harpon*, meaning a barbed spear) and the suffix "-er" (meaning a person who). A harpooner is a person who uses a harpoon, typically for hunting large sea animals.
Think of a person who uses a 'barbed spear' ('harpoon') — the '-er' indicates that this person is the one doing the action.