These days, if we think of the word radical, various organisations might come into mind, of religious or political significance. A quick look at the dictionary (I used the Merriam Webster) gives the meaning as:
very new and different from what is traditional or ordinary
very basic and important
having extreme political or social views that are not shared by most people.
It came into English in the 14th century, but at that time it had quite a different meaning. Let’s take a look at an example from 1398. This is taken from John Trevisa’s translation into English of Bartholomaeus’s On the Properties of Things, (De proprietatibus rerum) which was a kind of early encyclopaedia.
Þe onyoun..haþ þer vnder oþere rootes..and þerby..radical humour is ysent in to al þe herbe.
The onion has other roots underneath and thereby a radical feeling is sent through all of it.
Here, the word is used to mean ‘pertaining to roots”. This makes sense, as the word was taken from Late Latin radicalis, meaning ‘of roots/ about roots/ having roots’. This comes from Latin radix, meaning ‘root’, and was formed from the genitive form radices.
As the roots are perceivably where a plant starts, it started to take on a more figurative meaning of basic’ or ‘origin’ as time went on.
To trace our word further back in time, we will go to another word that also has the same <ahem> root. This is of course radish.
Radish, meaning the vegetable, can be found in Old English as rǽdic. An example is in Leechdoms, Wortcunning and Starcraft of Early England:
Syle ðane rǽdic tó þicganne
A radish takes in a muddy place
The source of rǽdic is the same as that of radical: Latin radix. There are a number of cognates in other languages which have allowed us to trace it to Proto-Indo-European and the root *wrad, meaning none other than ‘root’. We can see examples in Greek ρίζα [riza], Gothic waurts, Old English wyrt and wrotan, Welsh gwraidd and others. You can read more on the word root here.
So, does this mean that a radish is radical? Or that if you are radical you are really a radish?! On the first point, given that a radish is a root, you could describe it as radical in the sense in which the word first entered English, although perhaps not with today’s generally understood meaning. The jury is still out on the second point!