The word 界限 is formed by combining two characters, 界 and 限, each of which independently carries the core meaning of a boundary, limit, or dividing line. 界 originally conveyed the idea of a border between territories or fields, while 限 emphasized a threshold, barrier, or point that cannot be passed. Their combination is a semantic one, where the two synonyms are joined to mutually reinforce and concretize a single, more emphatic concept, the definitive line that marks a division or the utmost extent of something. This process creates a compound whose meaning is the unified essence of both parts: a clear demarcation.