Tree snake (3)
I believe the answer is:
asp
This clue could be a double definition.
'tree' is the first definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'snake' is the second definition.
(asp is a kind of snake)
Can you help me to learn more?
(Other definitions for asp that I've seen before include "A glider's what's called for" , "Snake seen in a spa, strangely" , "Cleopatra's poisoner" , "Small viper" , "One secreting poison" .)