Terrarium pet (4)
I believe the answer is:
newt
'terrarium pet' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for newt that I've seen before include "Semiaquatic amphibian" , "Went to find a sort of eft" , "found in pond!" , "Ask" , "Amphibious creature" .)