Reptile quietly hiding in ground (8)
I believe the answer is:
terrapin
'reptile' is the definition.
(terrapin is a kind of reptile)
'quietly hiding in ground' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'hiding in' indicates putting letters inside.
'ground' becomes 'terrain' (I've seen this before).
'p' placed within 'terrain' is 'TERRAPIN'.
(Other definitions for terrapin that I've seen before include "Aquatic tortoise" , "Small freshwater turtle" , "Web-footed turtle" , "A reptile; a printer (anag.)" , "Partner I found for freshwater tortoise" .)