In peril at disturbing snake, perhaps (9)
I believe the answer is:
reptilian
'snake perhaps' is the definition.
(I know that snake is a type of diapsid)
'in peril at disturbing' is the wordplay.
'disturbing' indicates an anagram.
'in'+'peril'+'at'='inperilat'
'inperilat' with letters rearranged gives 'REPTILIAN'.
(Other definitions for reptilian that I've seen before include "like a lizard" , "Mean" , "Like a crocodile" , "Snake-like" , "Like a 27 [MONITOR]" .)