I was talking with Boring Code Guy yesterday about a new field to be added to a form. He "suggested" that I use a radio button to meet his requirements and went on to ask if I was impressed that he knew the name of them. I fibbed and told him I was. Then he wondered out loud why they were called "radio buttons"? I'd wondered this too and it wasn't until that moment that I'd had any ideas.
It suddenly occurred to me that they are like the buttons on old-style transistor radio sets? You don't see these kind of buttons in the real world much nowadays, but we had them on the radio in the first car I remember my parents owning. My dad still has them on his Roberts radio (to whom his brand loyalty exists merely because they share their name). In this photo you can see the radio has four buttons on top. One - and only ever one - is pressed down. Press another and the other one will pop back up.
This is probably as much of a no-brainer to most of you as is where Check Boxes get their name, but it was something of a revelation for me. I'm kicking myself for not having realised this sooner.