序
xù · HSK 7
order
🔢 广 (building/roof) + 予 (give); the hall's side rooms laid out in a row, hence order/sequence
序 first named the east-west wings of a hall — rooms arranged in a fixed row under one roof. That fixed arrangement gave the wider sense of order and sequence, and a preface is the text placed first in line.
序 — 广 radical (shelter) + 予 (give/I)
Originally depicted the side walls or wings of a building under the 广 (shelter) radical, with 予 serving as the phonetic component. From 'side wall' it extended to mean 'sequence' or 'order,' as walls were arranged in succession. Today it commonly means 'order,' 'sequence,' or 'preface.'