Transmission by steam? (5)
I believe the answer is:
radio
This clue might be a double definition.
'transmission' is the first definition.
(radio is a kind of transmission)
'steam?' is the second definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'by' is the link.
Can you help me to learn more?
(Other definitions for radio that I've seen before include "Transmit" , "Broadcast receiver" , "Receiving device" , "Receiving set" , "means of communication" .)