Origin

The character combines heart or mind (the bottom component) with a sound hint (the top component that suggests the pronunciation nin). The meaning "endure" comes from the idea of keeping difficult feelings hidden in your heart—you bear suffering in silence without letting it show. The sound component provides a phonetic clue to how the character is pronounced rather than contributing to the meaning. Over time, this sense of hidden endurance expanded to include related meanings like "conceal" and "spy," since both involve keeping things secret or working unseen.