IPA: //ˈpædəlbɔːrd//
KK: /ˈpædəlˌbɔrd/
A long, narrow board that floats on water and is used for surfing or paddling.
She enjoyed paddleboarding on the calm lake during the summer.
Paddleboard is formed from "paddle" (from Middle English *padel*, meaning a tool for propelling a boat) and "board" (from Old English *bord*, meaning a flat piece of wood). The word describes a flat piece of wood used with a tool to propel oneself on water.
Think of using a 'tool' ('paddle') to move on a 'flat piece of wood' ('board') on water — that's what a paddleboard is.