Non-venomous snake (6)
I believe the answer is:
python
'non-venomous snake' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for python that I've seen before include "Large non-venomous snake" , "Heavy-bodied snake" , "Large constricting snake" , "crawler" , "Large snake that strangles its prey" .)