After some research, I found two reasonable explanations. But, IMHO, the two should be compiled as the following: > **老** is a prefix that is added to make **虎** and **鼠** easier to pronounce; besides, it implies that people respect **虎** and fear **鼠**. The two explanations as follow: ---------- ##Affix for smooth pronunciation## In the Classical Chinese era, texts were concise and some, if not most, of the words were one-character words. Yet, in colloquial context, people prepended/appended affixes to make the words easier to pronounce. These "new" words then became widely accepted and conventional. Some common affixes and their associated words: - **子(suffix)** > 獅子、兔子、鴨子、猴子、鏡子、桌子、椅子、房子、筷子、刀子... > lion, rabbit, duck, monkey, mirror, table, chair, house, chopsticks, knife... - **老(prefix)** > 老虎、老鼠、老鷹、老師... > tiger, rat, hawk, teacher... - **頭(suffix)** > 甜頭、苦頭、舌頭、骨頭、石頭、木頭... > sweetness, suffering, tongue, bone, stone, wood... ##Affix with connotation## In Chinese, `老`, apart from `aged/experienced`, has the implicit, figurative meaning of `respected` because people respect elderly so as to comply with the social value. That said, people prepended `老` on the ones they respect. This is why `老虎` and `老師` are named the way they are. `老鼠`, on the other hand, has various interpretations. Some state that it fits to literal meaning of `老` – `old`. According to the `Compendium of Materia Medica(本草綱目)`, a medical book, rats have the longest life span. Such misunderstanding came from the impression that rats have a high rate of reproduction and have been around people back then for the longest time. Some argue that the `老` in `老鼠` implies the cunning characteristics of rats. This interpretation can also be applied to `鷹`. The rest argue that people chose `老` for `老鼠` to imply their fear toward rats. As to why `獅` is named `獅子` but not `老獅`, the reason is intuitive – to avoid conflicting pronunciation with `老師`.