It is the hypothetical source of/evidence for its existence is provided by: Sanskrit tarsayati "dries up;" Avestan tarshu- "dry, solid;" Greek teresesthai "to become or be dry," tersainein "to make dry;" Latin torrere "dry up, parch," terra "earth, land;" Gothic þaursus "dry, barren," Old High German thurri, German dürr, Old English þyrre "dry;" Old English þurstig "thirsty."
1830, noun use of neuter of Latin aquarius "pertaining to water," as a noun, "water-carrier," genitive of aqua "water" (from PIE root *akwa- "water"). The word existed in Latin, but there it meant "drinking place for cattle." Originally especially for an artificial pond growing aquatic plants; of indoor "ocean gardens" by 1853. The Victorian mania for indoor aquariums began with the book "The Aquarium," published 1854 by English naturalist Philip Henry Gosse. An earlier attempt at a name for "fish tank" was marine vivarium.
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Definitions of terrarium from WordNet
a vivarium in which selected living plants are kept and observed;