Definition of country mouse in US English:

country mouse

noun

  • 1A mouse which lives in the countryside (originally as a character in fables).

  • 2(Frequently with allusion to one of Aesop's fables) a country dweller, especially one who is unfamiliar with urban life.

Origin

Mid 16th century. After classical Latin rusticus mūs (Horace), ancient Greek μῦς ἀρουραῖος (Aesop).