By tracing the origins or etymology of words you can often uncover interesting stories. Many words in English, for example, come from other languages, and some took a very meandering path to get there, while the meanings of others has changed completely over time.
Walnuts have nothing to do with walls, instead their name comes from the Old English wealh-hnutu, meaning “foreign nut”. The word Welsh and the -wall in Cornwall come from the same root (wealh), which was used by Anglo-Saxons and other speakers of Germanic languages to refer to speakers of others Celtic languages and Latin. It is also the root of such names as Walloon, Vlach and the names of a number of other places and peoples in Europe. In Welsh walnuts are known as cneuen ffrengig (French nuts).
The practice of naming unfamiliar things as “foreign” or including their country of origin in their name is quite common in many different languages. In Thai, for example, tomato is มะเขือเทศ (ma-khuea thet), “foreign eggplant”, lemon is มะนาวเทศ (manao thet) “foreign lime”, and ostrich is นกกระจอกเทศ (nok kracok thet), “foreign sparrow”, while the English word peach comes from the Latin malum persicum or persian apple, and the Mandarin Chinese for walnut is 胡桃 (hútāo) or “barbarian peach”.
You never know what you’re going to discovering when you look into the origins of words, and being familiar with the roots of foreign words can help you to remember them.