単一
たんいつ · tanitsu · JLPT N1 · na-adj
single
☝️ 単一 = 単 (single, alone) + 一 (one): both parts mean one, so it means single or sole
一 — single horizontal stroke
一 is one of the simplest pictographs in Chinese, depicting a single horizontal line to represent the number one. It has retained essentially the same form since oracle bone script over 3,000 years ago. By extension it also means 'first,' 'whole,' or 'same.'