Definitions for radiosondeˈreɪ di oʊˌsɒnd
Random House Webster's College Dictionary
ra•di•o•sondeˈreɪ di oʊˌsɒnd(n.)
an instrument carried aloft by balloon to transmit meteorological data by radio.
Origin of radiosonde:
A miniature radio carried aloft by an unmanned balloon to broadcast the pressure, temperature, and relative humidity of the upper air and to automatically transmit that information to the ground.