What is the X in X-mas?
c.1600, "game park," from Latin vivarium "enclosure for live game, park, warren, preserve, fish pond," neuter singular of vivarius, from vivus "alive, living" (see vivid). Meaning "glass bowl for studying living creatures" is from 1853.
enclosure with glass sides, and sometimes a glass top, arranged for keeping plants or terrestrial or semi-terrestrial animals indoors. The purpose may be decoration, scientific observation, or plant or animal propagation