To be honest, this wasn’t at the top of my list of queries to be answered until I read this article in the BBC Magazine. Both radical and radish are derived from the Latin word radix, which appropriately means root.
There was a time when being thought a radical was an honourable thing – reformers who set out to correct injustice at its root – although these days it has a more negative connotation of extremism.
As for the humble radish, it seems to be one of the words of Latin adopted by Anglo-Saxon quite early, appearing as redic or raedic.
And speaking of unexpected linguistic connection in the salad bowl, we have the word salad itself and the salacious. Both are derived from the Roman love of salt – salata, vegetables dressed with salt, and salax (literally ‘salted’) to describe a person in love which is the origin of salacious.
The English language is a mysterious thing!