第
dì · HSK 1
det.: marker of ordinal numerals
🏛️ 竹 bamboo + 弟 younger brother — bamboo tags numbered in order
第 marks ordinal numbers (第一 = first, 第二 = second). The 竹 (bamboo) radical on top recalls bamboo slips numbered in sequence; 弟 below gives the sound dì. Also means residence or mansion in classical use.
第 — bamboo radical 竹 (⺮) + 弟 'younger brother'
Originally written with 弟, which depicted a cord wound in order around a stake — implying sequence or order. The bamboo radical 竹 was later added (because bamboo strips were used for numbered tallies and documents), giving 第 the meaning of ordinal number, sequence, or rank.