Reptile that might not be what it appears to be (9)
I believe the answer is:
chameleon
I believe this is a double definition.
'reptile' is the first definition.
(chameleon is a kind of reptile)
'that might not be what it appears to be' is the second definition.
(chameleon can mean an inconstant person)
(Other definitions for chameleon that I've seen before include "Animal that changes colour" , "Lizard that can change colour to match surroundings" , "Self-camouflaging lizard" , "person who's changeable" , "Variable-colour reptile" .)