An Etymological Dictionary of Astronomy and Astrophysics

1. An enclosure, usually made with bars or wire, for keeping birds or wild animals.
   

2. An enclosed structure resembling a cage. → observer’s cage, → Faraday cage.

Etymology (EN): M.E. from O.Fr. cage, from L. cavea “hollow place, enclosure for animals,” cognate with Pers. kâv “hollow,” → concave.

Etymology (PE): Qafas “cage,” of unknown origin.