the.com/runner

means A person who runs, especially habitually or for sport — or by extension, something that moves, operates, or competes on someone's behalf, like a messenger or a candidate.

from Straightforward Old English stock: 'run' (rinnan/iernan in its older forms, tangled up with Old Norse rinna) plus the agent suffix '-er,' which has been turning verbs into doers since medieval English. The verb itself traces back to a very old Germanic root for flowing or rapid movement — the same deep well that gives related Germanic languages their own 'run' words. The extended senses (a smuggler's runner, a rug runner, a plant sending out runners) all ride on the same core idea: something that moves along, covers ground, or carries something forward.