Amphibian went astray (4)
I believe the answer is:
newt
'amphibian' is the definition.
(I know that newt is a type of salamander)
'went astray' is the wordplay.
'astray' is an anagram indicator.
'went' with letters rearranged gives 'NEWT'.
(Other definitions for newt that I've seen before include "Amphibian such as the salamander" , "Went (anag.)" , "Amphibious salamander" , "Amphibian - a Ken Livingstone pet?" , "Scientist" .)