Viper (5)
I believe the answer is:
adder
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">viper</span>' is the definition.<br/ ><span class="explanation-format__explanation">(adder is a kind of viper)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for adder that I've seen before include "a poisonous type" , "venomous creature" , "Totting snake" , "Viper common in northern Eurasia" , "Snake (like an abacus?)" .)