This snake counts? (5)

I believe the answer is:

adder

'this snake counts?' is the definition.
(I've seen this in another clue)

This is all the clue.

(Other definitions for adder that I've seen before include "Reptilian" , "Something you have to reckon with" , "Mathematical reptile" , "Venomous type" , "Poisonous Brit. snake" .)

I've seen this clue in The Sun, the Universal and the USA Today.

Want a hint initially instead of a full solution? Install my app