Liberal Dictionary English Dictionary
Trademark.
- a brand name for a telephonic device with a highly sensitive transmitter obviating the necessity of a mouthpiece: used for listening to conversations secretly or obtaining a record of them.
noun
- trademark a telephonic instrument for secretly monitoring or recording conversations by means of a small, sensitive, and often concealed microphone
patented 1907 in U.S. by K.M. Turner and W. Donnan, from dictation + -graph “instrument for recording; something written.”