Three might put you to sleep (5)
I believe the answer is:
ether
'sleep' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'three might put you' is the wordplay.
'three' can be anagrammed to 'ETHER'.
However, I am not clear how the anagram is indicated.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for ether that I've seen before include "Volatile organic liquid once used as a general anaesthetic" , "Anaesthetic is, strangely, there" , "Anaesthetic liquid; clear sky" , "Light liquid used as anaesthetic" , "Colourless liquid used as a solvent" .)