The word 永久 is formed through the conceptual fusion of its two constituent characters: 永, which pictographically suggests an endless, flowing stream and carries the core idea of "perpetuity" or "unceasing continuity", and 久, which depicts a figure with a curative moxa treatment and embodies the abstract concept of "a long duration in time". By combining these, the compound does not simply list two ideas but synthesizes them into a single, intensified concept where the sense of endless flow (永) inherently characterizes the extended duration (久), thereby creating the holistic meaning of "permanent" or "everlasting".