The word 老鼠 is formed by combining the character 老 (lǎo), which literally means "old", with 鼠 (shǔ), which means "rodent" or "mouse". In this context, 老 does not refer to age but functions as a familiar, almost colloquial prefix that can denote commonness, conventionality, or even a touch of endearment or notoriety. This formation mirrors other animal names like 老虎 (lǎohǔ, tiger), where 老 attaches to the core animal term (鼠) to create the standard, everyday name for the creature, subtly embedding it into common language and perception as a familiar, recognized entity.