界限
jièxiàn · HSK 7
boundary
🚧 界限 = 界 boundary/realm + 限 limit, doubled up to mean a hard dividing line
Both characters already mean edge or restriction: 界 marks a realm or border, 限 caps how far you can go. Stacking the two synonyms drives home the idea of a fixed bound or demarcation line that you cannot cross.
界 — field 田 + scope 介
界 combines 田 (field) as the semantic component with 介 (jiè) as the phonetic. The original sense referred to boundaries between fields, then broadened to any border, limit, or realm — yielding modern meanings like 'world' (世界) and 'boundary' (边界).
限 — mound radical 阝 + 艮 (phonetic)
限 combines the 阝 (mound/hill) radical on the left with 艮 on the right, which provides the sound. The mound element suggests a boundary or barrier formed by terrain, and the character came to mean 'limit' or 'boundary' — the edge one cannot cross.