Three is an odd number (5)
I believe the answer is:
ether
'number' is the definition.
(anaesthetic, something which numbs)
'three is an odd' is the wordplay.
'three' can be anagrammed to 'ETHER'.
However, I am not sure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for ether that I've seen before include "Anaesthetic; clear sky (poetic)" , "Volatile solvent" , "Imaginary interstellar medium" , "The gas is there, oddly" , "Colourless volatile highly inflammable liquid" .)