簡素
かんそ · kanso · JLPT N1 · na-adj
simplicity
簡素 = 簡 (simple) + 素 (plain, bare): simple and unadorned
素 also means raw or undyed, as in 素顔 (bare face). Put the two together and you get something stripped down to essentials.
素 — silk 糸 + sheng 𠂹 (hanging threads)
Originally depicted raw, undyed silk hanging to dry, with the silk radical 糸 below and strands above. From this came the meaning 'plain, unadorned, white,' then extended to 'basic element' or 'plain/simple' in general. The 'vegetarian' sense developed later from the idea of plain, unembellished food.