Skin sizeable amphibian (3)
I believe the answer is:
eft
'amphibian' is the definition.
(eft is a kind of amphibian)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for eft that I've seen before include "Young newt" , "Little creature" , "Slimy creature" , "Kind of newt found in clefts" , "Swimmer with feeble legs" .)