Viper, for example (5)
I believe the answer is:
snake
'viper for example' is the definition.
(I know that viper is a type of snake)
This is all the clue.
(Other definitions for snake that I've seen before include "Part of plant or hair" , "For instance, adder" , "Slithering reptile" , "Wind" , "Move sinuously" .)