Amphibian that we notice partially retreating (4)
I believe the answer is:
newt
'amphibian' is the definition.
(I know that newt is a type of salamander)
'that we notice partially retreating' is the wordplay.
'partially' indicates a hidden word.
'retreating' shows that the letters should be reversed in order.
'twen' is hidden in the letters of 'that we notice'.
'twen' back-to-front is 'NEWT'.
(Other definitions for newt that I've seen before include "legless for a start" , "The epitome of drunkenness" , "Amphibian such as the salamander" , "Went to find kind of water lizard" , "Went (anag.)" .)