almost wrote "where are the wheels of that plant" but something about that just didn't seem right
In this case, thinktiu as that specific plant, pointing out, and not just any plant.
Where does "radiko" come from? And how do I get to know an Esperanto word's origin?
I got this file https://archive.org/download/EsperantoEtymologicalDictionary/Esperanto.doc which I find pretty useful.