the.com/resonator guitar

means A guitar whose sound comes from one or more spun-metal cones (resonators) mounted in the body, amplifying the strings' vibration mechanically instead of relying on a wooden soundboard alone.

from Born in the late 1920s when guitarists needed more volume to compete with horns and drums in dance bands, long before electric amplification existed. Slovak-American craftsmen (brothers named Dopyera, who went on to found National and later Dobro) borrowed a trick from banjo and gramophone speaker design — a thin, cone-shaped metal diaphragm that vibrates like a speaker cone — and bolted it into a guitar body to mechanically amplify the strings. The name 'resonator' is just plain engineering language: the cone resonates, so the guitar got called by what it does.