Note the amphibian is adroit (4)
I believe the answer is:
deft
'adroit' is the definition.
(I've seen this before)
'note the amphibian' is the wordplay.
'note' becomes 'd' (musical note).
'the amphibian' becomes 'eft' (eft is a kind of amphibian).
'd'+'eft'='DEFT'
'is' acts as a link.
(Other definitions for deft that I've seen before include "Quick and dexterous" , "Handy" , "Clever" , "Proficient" , "Quick and skilful in movement" .)