同一
tóng yī · HSK 6
identical
🟰 tóng = same, yī = one — same-as-one, totally identical
Both characters reinforce unity: 同 (same/together) plus 一 (one) literally says 'same one.' If two things are tóng yī, they are not just similar — they are one and the same thing.
同 — 冂 enclosure + 一 + 口 mouth
Originally depicted multiple mouths gathered under one cover or enclosure, suggesting people speaking together in agreement. From this image of voices joining, it came to mean 'same,' 'together,' or 'alike.' The shared cover symbolizes unity.
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.'